Btrfs: deal with errors from updating the tree log

[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / kernel / perf_event.c

/*
 * Performance events core code:
 *
 *  Copyright (C) 2008 Thomas Gleixner <tglx@linutronix.de>
 *  Copyright (C) 2008-2009 Red Hat, Inc., Ingo Molnar
 *  Copyright (C) 2008-2009 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
 *  Copyright  ©  2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
 *
 * For licensing details see kernel-base/COPYING
 */

#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/cpu.h>
#include <linux/smp.h>
#include <linux/file.h>
#include <linux/poll.h>
#include <linux/slab.h>
#include <linux/hash.h>
#include <linux/sysfs.h>
#include <linux/dcache.h>
#include <linux/percpu.h>
#include <linux/ptrace.h>
#include <linux/vmstat.h>
#include <linux/vmalloc.h>
#include <linux/hardirq.h>
#include <linux/rculist.h>
#include <linux/uaccess.h>
#include <linux/syscalls.h>
#include <linux/anon_inodes.h>
#include <linux/kernel_stat.h>
#include <linux/perf_event.h>
#include <linux/ftrace_event.h>
#include <linux/hw_breakpoint.h>

#include <asm/irq_regs.h>

/*
 * Each CPU has a list of per CPU events:
 */
static DEFINE_PER_CPU(struct perf_cpu_context, perf_cpu_context);

int perf_max_events __read_mostly = 1;
static int perf_reserved_percpu __read_mostly;
static int perf_overcommit __read_mostly = 1;

static atomic_t nr_events __read_mostly;
static atomic_t nr_mmap_events __read_mostly;
static atomic_t nr_comm_events __read_mostly;
static atomic_t nr_task_events __read_mostly;

/*
 * perf event paranoia level:
 *  -1 - not paranoid at all
 *   0 - disallow raw tracepoint access for unpriv
 *   1 - disallow cpu events for unpriv
 *   2 - disallow kernel profiling for unpriv
 */
int sysctl_perf_event_paranoid __read_mostly = 1;

int sysctl_perf_event_mlock __read_mostly = 512; /* 'free' kb per user */

/*
 * max perf event sample rate
 */
int sysctl_perf_event_sample_rate __read_mostly = 100000;

static atomic64_t perf_event_id;

/*
 * Lock for (sysadmin-configurable) event reservations:
 */
static DEFINE_SPINLOCK(perf_resource_lock);

/*
 * Architecture provided APIs - weak aliases:
 */
extern __weak const struct pmu *hw_perf_event_init(struct perf_event *event)
{
        return NULL;
}

void __weak hw_perf_disable(void)               { barrier(); }
void __weak hw_perf_enable(void)                { barrier(); }

void __weak perf_event_print_debug(void)        { }

static DEFINE_PER_CPU(int, perf_disable_count);

void perf_disable(void)
{
        if (!__get_cpu_var(perf_disable_count)++)
                hw_perf_disable();
}

void perf_enable(void)
{
        if (!--__get_cpu_var(perf_disable_count))
                hw_perf_enable();
}

static void get_ctx(struct perf_event_context *ctx)
{
        WARN_ON(!atomic_inc_not_zero(&ctx->refcount));
}

static void free_ctx(struct rcu_head *head)
{
        struct perf_event_context *ctx;

        ctx = container_of(head, struct perf_event_context, rcu_head);
        kfree(ctx);
}

static void put_ctx(struct perf_event_context *ctx)
{
        if (atomic_dec_and_test(&ctx->refcount)) {
                if (ctx->parent_ctx)
                        put_ctx(ctx->parent_ctx);
                if (ctx->task)
                        put_task_struct(ctx->task);
                call_rcu(&ctx->rcu_head, free_ctx);
        }
}

static void unclone_ctx(struct perf_event_context *ctx)
{
        if (ctx->parent_ctx) {
                put_ctx(ctx->parent_ctx);
                ctx->parent_ctx = NULL;
        }
}

/*
 * If we inherit events we want to return the parent event id
 * to userspace.
 */
static u64 primary_event_id(struct perf_event *event)
{
        u64 id = event->id;

        if (event->parent)
                id = event->parent->id;

        return id;
}

/*
 * Get the perf_event_context for a task and lock it.
 * This has to cope with with the fact that until it is locked,
 * the context could get moved to another task.
 */
static struct perf_event_context *
perf_lock_task_context(struct task_struct *task, unsigned long *flags)
{
        struct perf_event_context *ctx;

        rcu_read_lock();
 retry:
        ctx = rcu_dereference(task->perf_event_ctxp);
        if (ctx) {
                /*
                 * If this context is a clone of another, it might
                 * get swapped for another underneath us by
                 * perf_event_task_sched_out, though the
                 * rcu_read_lock() protects us from any context
                 * getting freed.  Lock the context and check if it
                 * got swapped before we could get the lock, and retry
                 * if so.  If we locked the right context, then it
                 * can't get swapped on us any more.
                 */
                raw_spin_lock_irqsave(&ctx->lock, *flags);
                if (ctx != rcu_dereference(task->perf_event_ctxp)) {
                        raw_spin_unlock_irqrestore(&ctx->lock, *flags);
                        goto retry;
                }

                if (!atomic_inc_not_zero(&ctx->refcount)) {
                        raw_spin_unlock_irqrestore(&ctx->lock, *flags);
                        ctx = NULL;
                }
        }
        rcu_read_unlock();
        return ctx;
}

/*
 * Get the context for a task and increment its pin_count so it
 * can't get swapped to another task.  This also increments its
 * reference count so that the context can't get freed.
 */
static struct perf_event_context *perf_pin_task_context(struct task_struct *task)
{
        struct perf_event_context *ctx;
        unsigned long flags;

        ctx = perf_lock_task_context(task, &flags);
        if (ctx) {
                ++ctx->pin_count;
                raw_spin_unlock_irqrestore(&ctx->lock, flags);
        }
        return ctx;
}

static void perf_unpin_context(struct perf_event_context *ctx)
{
        unsigned long flags;

        raw_spin_lock_irqsave(&ctx->lock, flags);
        --ctx->pin_count;
        raw_spin_unlock_irqrestore(&ctx->lock, flags);
        put_ctx(ctx);
}

static inline u64 perf_clock(void)
{
        return local_clock();
}

/*
 * Update the record of the current time in a context.
 */
static void update_context_time(struct perf_event_context *ctx)
{
        u64 now = perf_clock();

        ctx->time += now - ctx->timestamp;
        ctx->timestamp = now;
}

/*
 * Update the total_time_enabled and total_time_running fields for a event.
 */
static void update_event_times(struct perf_event *event)
{
        struct perf_event_context *ctx = event->ctx;
        u64 run_end;

        if (event->state < PERF_EVENT_STATE_INACTIVE ||
            event->group_leader->state < PERF_EVENT_STATE_INACTIVE)
                return;

        if (ctx->is_active)
                run_end = ctx->time;
        else
                run_end = event->tstamp_stopped;

        event->total_time_enabled = run_end - event->tstamp_enabled;

        if (event->state == PERF_EVENT_STATE_INACTIVE)
                run_end = event->tstamp_stopped;
        else
                run_end = ctx->time;

        event->total_time_running = run_end - event->tstamp_running;
}

/*
 * Update total_time_enabled and total_time_running for all events in a group.
 */
static void update_group_times(struct perf_event *leader)
{
        struct perf_event *event;

        update_event_times(leader);
        list_for_each_entry(event, &leader->sibling_list, group_entry)
                update_event_times(event);
}

static struct list_head *
ctx_group_list(struct perf_event *event, struct perf_event_context *ctx)
{
        if (event->attr.pinned)
                return &ctx->pinned_groups;
        else
                return &ctx->flexible_groups;
}

/*
 * Add a event from the lists for its context.
 * Must be called with ctx->mutex and ctx->lock held.
 */
static void
list_add_event(struct perf_event *event, struct perf_event_context *ctx)
{
        WARN_ON_ONCE(event->attach_state & PERF_ATTACH_CONTEXT);
        event->attach_state |= PERF_ATTACH_CONTEXT;

        /*
         * If we're a stand alone event or group leader, we go to the context
         * list, group events are kept attached to the group so that
         * perf_group_detach can, at all times, locate all siblings.
         */
        if (event->group_leader == event) {
                struct list_head *list;

                if (is_software_event(event))
                        event->group_flags |= PERF_GROUP_SOFTWARE;

                list = ctx_group_list(event, ctx);
                list_add_tail(&event->group_entry, list);
        }

        list_add_rcu(&event->event_entry, &ctx->event_list);
        ctx->nr_events++;
        if (event->attr.inherit_stat)
                ctx->nr_stat++;
}

static void perf_group_attach(struct perf_event *event)
{
        struct perf_event *group_leader = event->group_leader;

        WARN_ON_ONCE(event->attach_state & PERF_ATTACH_GROUP);
        event->attach_state |= PERF_ATTACH_GROUP;

        if (group_leader == event)
                return;

        if (group_leader->group_flags & PERF_GROUP_SOFTWARE &&
                        !is_software_event(event))
                group_leader->group_flags &= ~PERF_GROUP_SOFTWARE;

        list_add_tail(&event->group_entry, &group_leader->sibling_list);
        group_leader->nr_siblings++;
}

/*
 * Remove a event from the lists for its context.
 * Must be called with ctx->mutex and ctx->lock held.
 */
static void
list_del_event(struct perf_event *event, struct perf_event_context *ctx)
{
        /*
         * We can have double detach due to exit/hot-unplug + close.
         */
        if (!(event->attach_state & PERF_ATTACH_CONTEXT))
                return;

        event->attach_state &= ~PERF_ATTACH_CONTEXT;

        ctx->nr_events--;
        if (event->attr.inherit_stat)
                ctx->nr_stat--;

        list_del_rcu(&event->event_entry);

        if (event->group_leader == event)
                list_del_init(&event->group_entry);

        update_group_times(event);

        /*
         * If event was in error state, then keep it
         * that way, otherwise bogus counts will be
         * returned on read(). The only way to get out
         * of error state is by explicit re-enabling
         * of the event
         */
        if (event->state > PERF_EVENT_STATE_OFF)
                event->state = PERF_EVENT_STATE_OFF;
}

static void perf_group_detach(struct perf_event *event)
{
        struct perf_event *sibling, *tmp;
        struct list_head *list = NULL;

        /*
         * We can have double detach due to exit/hot-unplug + close.
         */
        if (!(event->attach_state & PERF_ATTACH_GROUP))
                return;

        event->attach_state &= ~PERF_ATTACH_GROUP;

        /*
         * If this is a sibling, remove it from its group.
         */
        if (event->group_leader != event) {
                list_del_init(&event->group_entry);
                event->group_leader->nr_siblings--;
                return;
        }

        if (!list_empty(&event->group_entry))
                list = &event->group_entry;

        /*
         * If this was a group event with sibling events then
         * upgrade the siblings to singleton events by adding them
         * to whatever list we are on.
         */
        list_for_each_entry_safe(sibling, tmp, &event->sibling_list, group_entry) {
                if (list)
                        list_move_tail(&sibling->group_entry, list);
                sibling->group_leader = sibling;

                /* Inherit group flags from the previous leader */
                sibling->group_flags = event->group_flags;
        }
}

static inline int
event_filter_match(struct perf_event *event)
{
        return event->cpu == -1 || event->cpu == smp_processor_id();
}

static void
event_sched_out(struct perf_event *event,
                  struct perf_cpu_context *cpuctx,
                  struct perf_event_context *ctx)
{
        u64 delta;
        /*
         * An event which could not be activated because of
         * filter mismatch still needs to have its timings
         * maintained, otherwise bogus information is return
         * via read() for time_enabled, time_running:
         */
        if (event->state == PERF_EVENT_STATE_INACTIVE
            && !event_filter_match(event)) {
                delta = ctx->time - event->tstamp_stopped;
                event->tstamp_running += delta;
                event->tstamp_stopped = ctx->time;
        }

        if (event->state != PERF_EVENT_STATE_ACTIVE)
                return;

        event->state = PERF_EVENT_STATE_INACTIVE;
        if (event->pending_disable) {
                event->pending_disable = 0;
                event->state = PERF_EVENT_STATE_OFF;
        }
        event->tstamp_stopped = ctx->time;
        event->pmu->disable(event);
        event->oncpu = -1;

        if (!is_software_event(event))
                cpuctx->active_oncpu--;
        ctx->nr_active--;
        if (event->attr.exclusive || !cpuctx->active_oncpu)
                cpuctx->exclusive = 0;
}

static void
group_sched_out(struct perf_event *group_event,
                struct perf_cpu_context *cpuctx,
                struct perf_event_context *ctx)
{
        struct perf_event *event;
        int state = group_event->state;

        event_sched_out(group_event, cpuctx, ctx);

        /*
         * Schedule out siblings (if any):
         */
        list_for_each_entry(event, &group_event->sibling_list, group_entry)
                event_sched_out(event, cpuctx, ctx);

        if (state == PERF_EVENT_STATE_ACTIVE && group_event->attr.exclusive)
                cpuctx->exclusive = 0;
}

/*
 * Cross CPU call to remove a performance event
 *
 * We disable the event on the hardware level first. After that we
 * remove it from the context list.
 */
static void __perf_event_remove_from_context(void *info)
{
        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
        struct perf_event *event = info;
        struct perf_event_context *ctx = event->ctx;

        /*
         * If this is a task context, we need to check whether it is
         * the current task context of this cpu. If not it has been
         * scheduled out before the smp call arrived.
         */
        if (ctx->task && cpuctx->task_ctx != ctx)
                return;

        raw_spin_lock(&ctx->lock);
        /*
         * Protect the list operation against NMI by disabling the
         * events on a global level.
         */
        perf_disable();

        event_sched_out(event, cpuctx, ctx);

        list_del_event(event, ctx);

        if (!ctx->task) {
                /*
                 * Allow more per task events with respect to the
                 * reservation:
                 */
                cpuctx->max_pertask =
                        min(perf_max_events - ctx->nr_events,
                            perf_max_events - perf_reserved_percpu);
        }

        perf_enable();
        raw_spin_unlock(&ctx->lock);
}


/*
 * Remove the event from a task's (or a CPU's) list of events.
 *
 * Must be called with ctx->mutex held.
 *
 * CPU events are removed with a smp call. For task events we only
 * call when the task is on a CPU.
 *
 * If event->ctx is a cloned context, callers must make sure that
 * every task struct that event->ctx->task could possibly point to
 * remains valid.  This is OK when called from perf_release since
 * that only calls us on the top-level context, which can't be a clone.
 * When called from perf_event_exit_task, it's OK because the
 * context has been detached from its task.
 */
static void perf_event_remove_from_context(struct perf_event *event)
{
        struct perf_event_context *ctx = event->ctx;
        struct task_struct *task = ctx->task;

        if (!task) {
                /*
                 * Per cpu events are removed via an smp call and
                 * the removal is always successful.
                 */
                smp_call_function_single(event->cpu,
                                         __perf_event_remove_from_context,
                                         event, 1);
                return;
        }

retry:
        task_oncpu_function_call(task, __perf_event_remove_from_context,
                                 event);

        raw_spin_lock_irq(&ctx->lock);
        /*
         * If the context is active we need to retry the smp call.
         */
        if (ctx->nr_active && !list_empty(&event->group_entry)) {
                raw_spin_unlock_irq(&ctx->lock);
                goto retry;
        }

        /*
         * The lock prevents that this context is scheduled in so we
         * can remove the event safely, if the call above did not
         * succeed.
         */
        if (!list_empty(&event->group_entry))
                list_del_event(event, ctx);
        raw_spin_unlock_irq(&ctx->lock);
}

/*
 * Cross CPU call to disable a performance event
 */
static void __perf_event_disable(void *info)
{
        struct perf_event *event = info;
        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
        struct perf_event_context *ctx = event->ctx;

        /*
         * If this is a per-task event, need to check whether this
         * event's task is the current task on this cpu.
         */
        if (ctx->task && cpuctx->task_ctx != ctx)
                return;

        raw_spin_lock(&ctx->lock);

        /*
         * If the event is on, turn it off.
         * If it is in error state, leave it in error state.
         */
        if (event->state >= PERF_EVENT_STATE_INACTIVE) {
                update_context_time(ctx);
                update_group_times(event);
                if (event == event->group_leader)
                        group_sched_out(event, cpuctx, ctx);
                else
                        event_sched_out(event, cpuctx, ctx);
                event->state = PERF_EVENT_STATE_OFF;
        }

        raw_spin_unlock(&ctx->lock);
}

/*
 * Disable a event.
 *
 * If event->ctx is a cloned context, callers must make sure that
 * every task struct that event->ctx->task could possibly point to
 * remains valid.  This condition is satisifed when called through
 * perf_event_for_each_child or perf_event_for_each because they
 * hold the top-level event's child_mutex, so any descendant that
 * goes to exit will block in sync_child_event.
 * When called from perf_pending_event it's OK because event->ctx
 * is the current context on this CPU and preemption is disabled,
 * hence we can't get into perf_event_task_sched_out for this context.
 */
void perf_event_disable(struct perf_event *event)
{
        struct perf_event_context *ctx = event->ctx;
        struct task_struct *task = ctx->task;

        if (!task) {
                /*
                 * Disable the event on the cpu that it's on
                 */
                smp_call_function_single(event->cpu, __perf_event_disable,
                                         event, 1);
                return;
        }

 retry:
        task_oncpu_function_call(task, __perf_event_disable, event);

        raw_spin_lock_irq(&ctx->lock);
        /*
         * If the event is still active, we need to retry the cross-call.
         */
        if (event->state == PERF_EVENT_STATE_ACTIVE) {
                raw_spin_unlock_irq(&ctx->lock);
                goto retry;
        }

        /*
         * Since we have the lock this context can't be scheduled
         * in, so we can change the state safely.
         */
        if (event->state == PERF_EVENT_STATE_INACTIVE) {
                update_group_times(event);
                event->state = PERF_EVENT_STATE_OFF;
        }

        raw_spin_unlock_irq(&ctx->lock);
}

static int
event_sched_in(struct perf_event *event,
                 struct perf_cpu_context *cpuctx,
                 struct perf_event_context *ctx)
{
        if (event->state <= PERF_EVENT_STATE_OFF)
                return 0;

        event->state = PERF_EVENT_STATE_ACTIVE;
        event->oncpu = smp_processor_id();
        /*
         * The new state must be visible before we turn it on in the hardware:
         */
        smp_wmb();

        if (event->pmu->enable(event)) {
                event->state = PERF_EVENT_STATE_INACTIVE;
                event->oncpu = -1;
                return -EAGAIN;
        }

        event->tstamp_running += ctx->time - event->tstamp_stopped;

        if (!is_software_event(event))
                cpuctx->active_oncpu++;
        ctx->nr_active++;

        if (event->attr.exclusive)
                cpuctx->exclusive = 1;

        return 0;
}

static int
group_sched_in(struct perf_event *group_event,
               struct perf_cpu_context *cpuctx,
               struct perf_event_context *ctx)
{
        struct perf_event *event, *partial_group = NULL;
        const struct pmu *pmu = group_event->pmu;
        bool txn = false;

        if (group_event->state == PERF_EVENT_STATE_OFF)
                return 0;

        /* Check if group transaction availabe */
        if (pmu->start_txn)
                txn = true;

        if (txn)
                pmu->start_txn(pmu);

        if (event_sched_in(group_event, cpuctx, ctx)) {
                if (txn)
                        pmu->cancel_txn(pmu);
                return -EAGAIN;
        }

        /*
         * Schedule in siblings as one group (if any):
         */
        list_for_each_entry(event, &group_event->sibling_list, group_entry) {
                if (event_sched_in(event, cpuctx, ctx)) {
                        partial_group = event;
                        goto group_error;
                }
        }

        if (!txn || !pmu->commit_txn(pmu))
                return 0;

group_error:
        /*
         * Groups can be scheduled in as one unit only, so undo any
         * partial group before returning:
         */
        list_for_each_entry(event, &group_event->sibling_list, group_entry) {
                if (event == partial_group)
                        break;
                event_sched_out(event, cpuctx, ctx);
        }
        event_sched_out(group_event, cpuctx, ctx);

        if (txn)
                pmu->cancel_txn(pmu);

        return -EAGAIN;
}

/*
 * Work out whether we can put this event group on the CPU now.
 */
static int group_can_go_on(struct perf_event *event,
                           struct perf_cpu_context *cpuctx,
                           int can_add_hw)
{
        /*
         * Groups consisting entirely of software events can always go on.
         */
        if (event->group_flags & PERF_GROUP_SOFTWARE)
                return 1;
        /*
         * If an exclusive group is already on, no other hardware
         * events can go on.
         */
        if (cpuctx->exclusive)
                return 0;
        /*
         * If this group is exclusive and there are already
         * events on the CPU, it can't go on.
         */
        if (event->attr.exclusive && cpuctx->active_oncpu)
                return 0;
        /*
         * Otherwise, try to add it if all previous groups were able
         * to go on.
         */
        return can_add_hw;
}

static void add_event_to_ctx(struct perf_event *event,
                               struct perf_event_context *ctx)
{
        list_add_event(event, ctx);
        perf_group_attach(event);
        event->tstamp_enabled = ctx->time;
        event->tstamp_running = ctx->time;
        event->tstamp_stopped = ctx->time;
}

/*
 * Cross CPU call to install and enable a performance event
 *
 * Must be called with ctx->mutex held
 */
static void __perf_install_in_context(void *info)
{
        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
        struct perf_event *event = info;
        struct perf_event_context *ctx = event->ctx;
        struct perf_event *leader = event->group_leader;
        int err;

        /*
         * If this is a task context, we need to check whether it is
         * the current task context of this cpu. If not it has been
         * scheduled out before the smp call arrived.
         * Or possibly this is the right context but it isn't
         * on this cpu because it had no events.
         */
        if (ctx->task && cpuctx->task_ctx != ctx) {
                if (cpuctx->task_ctx || ctx->task != current)
                        return;
                cpuctx->task_ctx = ctx;
        }

        raw_spin_lock(&ctx->lock);
        ctx->is_active = 1;
        update_context_time(ctx);

        /*
         * Protect the list operation against NMI by disabling the
         * events on a global level. NOP for non NMI based events.
         */
        perf_disable();

        add_event_to_ctx(event, ctx);

        if (event->cpu != -1 && event->cpu != smp_processor_id())
                goto unlock;

        /*
         * Don't put the event on if it is disabled or if
         * it is in a group and the group isn't on.
         */
        if (event->state != PERF_EVENT_STATE_INACTIVE ||
            (leader != event && leader->state != PERF_EVENT_STATE_ACTIVE))
                goto unlock;

        /*
         * An exclusive event can't go on if there are already active
         * hardware events, and no hardware event can go on if there
         * is already an exclusive event on.
         */
        if (!group_can_go_on(event, cpuctx, 1))
                err = -EEXIST;
        else
                err = event_sched_in(event, cpuctx, ctx);

        if (err) {
                /*
                 * This event couldn't go on.  If it is in a group
                 * then we have to pull the whole group off.
                 * If the event group is pinned then put it in error state.
                 */
                if (leader != event)
                        group_sched_out(leader, cpuctx, ctx);
                if (leader->attr.pinned) {
                        update_group_times(leader);
                        leader->state = PERF_EVENT_STATE_ERROR;
                }
        }

        if (!err && !ctx->task && cpuctx->max_pertask)
                cpuctx->max_pertask--;

 unlock:
        perf_enable();

        raw_spin_unlock(&ctx->lock);
}

/*
 * Attach a performance event to a context
 *
 * First we add the event to the list with the hardware enable bit
 * in event->hw_config cleared.
 *
 * If the event is attached to a task which is on a CPU we use a smp
 * call to enable it in the task context. The task might have been
 * scheduled away, but we check this in the smp call again.
 *
 * Must be called with ctx->mutex held.
 */
static void
perf_install_in_context(struct perf_event_context *ctx,
                        struct perf_event *event,
                        int cpu)
{
        struct task_struct *task = ctx->task;

        if (!task) {
                /*
                 * Per cpu events are installed via an smp call and
                 * the install is always successful.
                 */
                smp_call_function_single(cpu, __perf_install_in_context,
                                         event, 1);
                return;
        }

retry:
        task_oncpu_function_call(task, __perf_install_in_context,
                                 event);

        raw_spin_lock_irq(&ctx->lock);
        /*
         * we need to retry the smp call.
         */
        if (ctx->is_active && list_empty(&event->group_entry)) {
                raw_spin_unlock_irq(&ctx->lock);
                goto retry;
        }

        /*
         * The lock prevents that this context is scheduled in so we
         * can add the event safely, if it the call above did not
         * succeed.
         */
        if (list_empty(&event->group_entry))
                add_event_to_ctx(event, ctx);
        raw_spin_unlock_irq(&ctx->lock);
}

/*
 * Put a event into inactive state and update time fields.
 * Enabling the leader of a group effectively enables all
 * the group members that aren't explicitly disabled, so we
 * have to update their ->tstamp_enabled also.
 * Note: this works for group members as well as group leaders
 * since the non-leader members' sibling_lists will be empty.
 */
static void __perf_event_mark_enabled(struct perf_event *event,
                                        struct perf_event_context *ctx)
{
        struct perf_event *sub;

        event->state = PERF_EVENT_STATE_INACTIVE;
        event->tstamp_enabled = ctx->time - event->total_time_enabled;
        list_for_each_entry(sub, &event->sibling_list, group_entry)
                if (sub->state >= PERF_EVENT_STATE_INACTIVE)
                        sub->tstamp_enabled =
                                ctx->time - sub->total_time_enabled;
}

/*
 * Cross CPU call to enable a performance event
 */
static void __perf_event_enable(void *info)
{
        struct perf_event *event = info;
        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
        struct perf_event_context *ctx = event->ctx;
        struct perf_event *leader = event->group_leader;
        int err;

        /*
         * If this is a per-task event, need to check whether this
         * event's task is the current task on this cpu.
         */
        if (ctx->task && cpuctx->task_ctx != ctx) {
                if (cpuctx->task_ctx || ctx->task != current)
                        return;
                cpuctx->task_ctx = ctx;
        }

        raw_spin_lock(&ctx->lock);
        ctx->is_active = 1;
        update_context_time(ctx);

        if (event->state >= PERF_EVENT_STATE_INACTIVE)
                goto unlock;
        __perf_event_mark_enabled(event, ctx);

        if (event->cpu != -1 && event->cpu != smp_processor_id())
                goto unlock;

        /*
         * If the event is in a group and isn't the group leader,
         * then don't put it on unless the group is on.
         */
        if (leader != event && leader->state != PERF_EVENT_STATE_ACTIVE)
                goto unlock;

        if (!group_can_go_on(event, cpuctx, 1)) {
                err = -EEXIST;
        } else {
                perf_disable();
                if (event == leader)
                        err = group_sched_in(event, cpuctx, ctx);
                else
                        err = event_sched_in(event, cpuctx, ctx);
                perf_enable();
        }

        if (err) {
                /*
                 * If this event can't go on and it's part of a
                 * group, then the whole group has to come off.
                 */
                if (leader != event)
                        group_sched_out(leader, cpuctx, ctx);
                if (leader->attr.pinned) {
                        update_group_times(leader);
                        leader->state = PERF_EVENT_STATE_ERROR;
                }
        }

 unlock:
        raw_spin_unlock(&ctx->lock);
}

/*
 * Enable a event.
 *
 * If event->ctx is a cloned context, callers must make sure that
 * every task struct that event->ctx->task could possibly point to
 * remains valid.  This condition is satisfied when called through
 * perf_event_for_each_child or perf_event_for_each as described
 * for perf_event_disable.
 */
void perf_event_enable(struct perf_event *event)
{
        struct perf_event_context *ctx = event->ctx;
        struct task_struct *task = ctx->task;

        if (!task) {
                /*
                 * Enable the event on the cpu that it's on
                 */
                smp_call_function_single(event->cpu, __perf_event_enable,
                                         event, 1);
                return;
        }

        raw_spin_lock_irq(&ctx->lock);
        if (event->state >= PERF_EVENT_STATE_INACTIVE)
                goto out;

        /*
         * If the event is in error state, clear that first.
         * That way, if we see the event in error state below, we
         * know that it has gone back into error state, as distinct
         * from the task having been scheduled away before the
         * cross-call arrived.
         */
        if (event->state == PERF_EVENT_STATE_ERROR)
                event->state = PERF_EVENT_STATE_OFF;

 retry:
        raw_spin_unlock_irq(&ctx->lock);
        task_oncpu_function_call(task, __perf_event_enable, event);

        raw_spin_lock_irq(&ctx->lock);

        /*
         * If the context is active and the event is still off,
         * we need to retry the cross-call.
         */
        if (ctx->is_active && event->state == PERF_EVENT_STATE_OFF)
                goto retry;

        /*
         * Since we have the lock this context can't be scheduled
         * in, so we can change the state safely.
         */
        if (event->state == PERF_EVENT_STATE_OFF)
                __perf_event_mark_enabled(event, ctx);

 out:
        raw_spin_unlock_irq(&ctx->lock);
}

static int perf_event_refresh(struct perf_event *event, int refresh)
{
        /*
         * not supported on inherited events
         */
        if (event->attr.inherit)
                return -EINVAL;

        atomic_add(refresh, &event->event_limit);
        perf_event_enable(event);

        return 0;
}

enum event_type_t {
        EVENT_FLEXIBLE = 0x1,
        EVENT_PINNED = 0x2,
        EVENT_ALL = EVENT_FLEXIBLE | EVENT_PINNED,
};

static void ctx_sched_out(struct perf_event_context *ctx,
                          struct perf_cpu_context *cpuctx,
                          enum event_type_t event_type)
{
        struct perf_event *event;

        raw_spin_lock(&ctx->lock);
        ctx->is_active = 0;
        if (likely(!ctx->nr_events))
                goto out;
        update_context_time(ctx);

        perf_disable();
        if (!ctx->nr_active)
                goto out_enable;

        if (event_type & EVENT_PINNED)
                list_for_each_entry(event, &ctx->pinned_groups, group_entry)
                        group_sched_out(event, cpuctx, ctx);

        if (event_type & EVENT_FLEXIBLE)
                list_for_each_entry(event, &ctx->flexible_groups, group_entry)
                        group_sched_out(event, cpuctx, ctx);

 out_enable:
        perf_enable();
 out:
        raw_spin_unlock(&ctx->lock);
}

/*
 * Test whether two contexts are equivalent, i.e. whether they
 * have both been cloned from the same version of the same context
 * and they both have the same number of enabled events.
 * If the number of enabled events is the same, then the set
 * of enabled events should be the same, because these are both
 * inherited contexts, therefore we can't access individual events
 * in them directly with an fd; we can only enable/disable all
 * events via prctl, or enable/disable all events in a family
 * via ioctl, which will have the same effect on both contexts.
 */
static int context_equiv(struct perf_event_context *ctx1,
                         struct perf_event_context *ctx2)
{
        return ctx1->parent_ctx && ctx1->parent_ctx == ctx2->parent_ctx
                && ctx1->parent_gen == ctx2->parent_gen
                && !ctx1->pin_count && !ctx2->pin_count;
}

static void __perf_event_sync_stat(struct perf_event *event,
                                     struct perf_event *next_event)
{
        u64 value;

        if (!event->attr.inherit_stat)
                return;

        /*
         * Update the event value, we cannot use perf_event_read()
         * because we're in the middle of a context switch and have IRQs
         * disabled, which upsets smp_call_function_single(), however
         * we know the event must be on the current CPU, therefore we
         * don't need to use it.
         */
        switch (event->state) {
        case PERF_EVENT_STATE_ACTIVE:
                event->pmu->read(event);
                /* fall-through */

        case PERF_EVENT_STATE_INACTIVE:
                update_event_times(event);
                break;

        default:
                break;
        }

        /*
         * In order to keep per-task stats reliable we need to flip the event
         * values when we flip the contexts.
         */
        value = local64_read(&next_event->count);
        value = local64_xchg(&event->count, value);
        local64_set(&next_event->count, value);

        swap(event->total_time_enabled, next_event->total_time_enabled);
        swap(event->total_time_running, next_event->total_time_running);

        /*
         * Since we swizzled the values, update the user visible data too.
         */
        perf_event_update_userpage(event);
        perf_event_update_userpage(next_event);
}

#define list_next_entry(pos, member) \
        list_entry(pos->member.next, typeof(*pos), member)

static void perf_event_sync_stat(struct perf_event_context *ctx,
                                   struct perf_event_context *next_ctx)
{
        struct perf_event *event, *next_event;

        if (!ctx->nr_stat)
                return;

        update_context_time(ctx);

        event = list_first_entry(&ctx->event_list,
                                   struct perf_event, event_entry);

        next_event = list_first_entry(&next_ctx->event_list,
                                        struct perf_event, event_entry);

        while (&event->event_entry != &ctx->event_list &&
               &next_event->event_entry != &next_ctx->event_list) {

                __perf_event_sync_stat(event, next_event);

                event = list_next_entry(event, event_entry);
                next_event = list_next_entry(next_event, event_entry);
        }
}

/*
 * Called from scheduler to remove the events of the current task,
 * with interrupts disabled.
 *
 * We stop each event and update the event value in event->count.
 *
 * This does not protect us against NMI, but disable()
 * sets the disabled bit in the control field of event _before_
 * accessing the event control register. If a NMI hits, then it will
 * not restart the event.
 */
void perf_event_task_sched_out(struct task_struct *task,
                                 struct task_struct *next)
{
        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
        struct perf_event_context *ctx = task->perf_event_ctxp;
        struct perf_event_context *next_ctx;
        struct perf_event_context *parent;
        int do_switch = 1;

        perf_sw_event(PERF_COUNT_SW_CONTEXT_SWITCHES, 1, 1, NULL, 0);

        if (likely(!ctx || !cpuctx->task_ctx))
                return;

        rcu_read_lock();
        parent = rcu_dereference(ctx->parent_ctx);
        next_ctx = next->perf_event_ctxp;
        if (parent && next_ctx &&
            rcu_dereference(next_ctx->parent_ctx) == parent) {
                /*
                 * Looks like the two contexts are clones, so we might be
                 * able to optimize the context switch.  We lock both
                 * contexts and check that they are clones under the
                 * lock (including re-checking that neither has been
                 * uncloned in the meantime).  It doesn't matter which
                 * order we take the locks because no other cpu could
                 * be trying to lock both of these tasks.
                 */
                raw_spin_lock(&ctx->lock);
                raw_spin_lock_nested(&next_ctx->lock, SINGLE_DEPTH_NESTING);
                if (context_equiv(ctx, next_ctx)) {
                        /*
                         * XXX do we need a memory barrier of sorts
                         * wrt to rcu_dereference() of perf_event_ctxp
                         */
                        task->perf_event_ctxp = next_ctx;
                        next->perf_event_ctxp = ctx;
                        ctx->task = next;
                        next_ctx->task = task;
                        do_switch = 0;

                        perf_event_sync_stat(ctx, next_ctx);
                }
                raw_spin_unlock(&next_ctx->lock);
                raw_spin_unlock(&ctx->lock);
        }
        rcu_read_unlock();

        if (do_switch) {
                ctx_sched_out(ctx, cpuctx, EVENT_ALL);
                cpuctx->task_ctx = NULL;
        }
}

static void task_ctx_sched_out(struct perf_event_context *ctx,
                               enum event_type_t event_type)
{
        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);

        if (!cpuctx->task_ctx)
                return;

        if (WARN_ON_ONCE(ctx != cpuctx->task_ctx))
                return;

        ctx_sched_out(ctx, cpuctx, event_type);
        cpuctx->task_ctx = NULL;
}

/*
 * Called with IRQs disabled
 */
static void __perf_event_task_sched_out(struct perf_event_context *ctx)
{
        task_ctx_sched_out(ctx, EVENT_ALL);
}

/*
 * Called with IRQs disabled
 */
static void cpu_ctx_sched_out(struct perf_cpu_context *cpuctx,
                              enum event_type_t event_type)
{
        ctx_sched_out(&cpuctx->ctx, cpuctx, event_type);
}

static void
ctx_pinned_sched_in(struct perf_event_context *ctx,
                    struct perf_cpu_context *cpuctx)
{
        struct perf_event *event;

        list_for_each_entry(event, &ctx->pinned_groups, group_entry) {
                if (event->state <= PERF_EVENT_STATE_OFF)
                        continue;
                if (event->cpu != -1 && event->cpu != smp_processor_id())
                        continue;

                if (group_can_go_on(event, cpuctx, 1))
                        group_sched_in(event, cpuctx, ctx);

                /*
                 * If this pinned group hasn't been scheduled,
                 * put it in error state.
                 */
                if (event->state == PERF_EVENT_STATE_INACTIVE) {
                        update_group_times(event);
                        event->state = PERF_EVENT_STATE_ERROR;
                }
        }
}

static void
ctx_flexible_sched_in(struct perf_event_context *ctx,
                      struct perf_cpu_context *cpuctx)
{
        struct perf_event *event;
        int can_add_hw = 1;

        list_for_each_entry(event, &ctx->flexible_groups, group_entry) {
                /* Ignore events in OFF or ERROR state */
                if (event->state <= PERF_EVENT_STATE_OFF)
                        continue;
                /*
                 * Listen to the 'cpu' scheduling filter constraint
                 * of events:
                 */
                if (event->cpu != -1 && event->cpu != smp_processor_id())
                        continue;

                if (group_can_go_on(event, cpuctx, can_add_hw))
                        if (group_sched_in(event, cpuctx, ctx))
                                can_add_hw = 0;
        }
}

static void
ctx_sched_in(struct perf_event_context *ctx,
             struct perf_cpu_context *cpuctx,
             enum event_type_t event_type)
{
        raw_spin_lock(&ctx->lock);
        ctx->is_active = 1;
        if (likely(!ctx->nr_events))
                goto out;

        ctx->timestamp = perf_clock();

        perf_disable();

        /*
         * First go through the list and put on any pinned groups
         * in order to give them the best chance of going on.
         */
        if (event_type & EVENT_PINNED)
                ctx_pinned_sched_in(ctx, cpuctx);

        /* Then walk through the lower prio flexible groups */
        if (event_type & EVENT_FLEXIBLE)
                ctx_flexible_sched_in(ctx, cpuctx);

        perf_enable();
 out:
        raw_spin_unlock(&ctx->lock);
}

static void cpu_ctx_sched_in(struct perf_cpu_context *cpuctx,
                             enum event_type_t event_type)
{
        struct perf_event_context *ctx = &cpuctx->ctx;

        ctx_sched_in(ctx, cpuctx, event_type);
}

static void task_ctx_sched_in(struct task_struct *task,
                              enum event_type_t event_type)
{
        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
        struct perf_event_context *ctx = task->perf_event_ctxp;

        if (likely(!ctx))
                return;
        if (cpuctx->task_ctx == ctx)
                return;
        ctx_sched_in(ctx, cpuctx, event_type);
        cpuctx->task_ctx = ctx;
}
/*
 * Called from scheduler to add the events of the current task
 * with interrupts disabled.
 *
 * We restore the event value and then enable it.
 *
 * This does not protect us against NMI, but enable()
 * sets the enabled bit in the control field of event _before_
 * accessing the event control register. If a NMI hits, then it will
 * keep the event running.
 */
void perf_event_task_sched_in(struct task_struct *task)
{
        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
        struct perf_event_context *ctx = task->perf_event_ctxp;

        if (likely(!ctx))
                return;

        if (cpuctx->task_ctx == ctx)
                return;

        perf_disable();

        /*
         * We want to keep the following priority order:
         * cpu pinned (that don't need to move), task pinned,
         * cpu flexible, task flexible.
         */
        cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE);

        ctx_sched_in(ctx, cpuctx, EVENT_PINNED);
        cpu_ctx_sched_in(cpuctx, EVENT_FLEXIBLE);
        ctx_sched_in(ctx, cpuctx, EVENT_FLEXIBLE);

        cpuctx->task_ctx = ctx;

        perf_enable();
}

#define MAX_INTERRUPTS (~0ULL)

static void perf_log_throttle(struct perf_event *event, int enable);

static u64 perf_calculate_period(struct perf_event *event, u64 nsec, u64 count)
{
        u64 frequency = event->attr.sample_freq;
        u64 sec = NSEC_PER_SEC;
        u64 divisor, dividend;

        int count_fls, nsec_fls, frequency_fls, sec_fls;

        count_fls = fls64(count);
        nsec_fls = fls64(nsec);
        frequency_fls = fls64(frequency);
        sec_fls = 30;

        /*
         * We got @count in @nsec, with a target of sample_freq HZ
         * the target period becomes:
         *
         *             @count * 10^9
         * period = -------------------
         *          @nsec * sample_freq
         *
         */

        /*
         * Reduce accuracy by one bit such that @a and @b converge
         * to a similar magnitude.
         */
#define REDUCE_FLS(a, b)                \
do {                                    \
        if (a##_fls > b##_fls) {        \
                a >>= 1;                \
                a##_fls--;              \
        } else {                        \
                b >>= 1;                \
                b##_fls--;              \
        }                               \
} while (0)

        /*
         * Reduce accuracy until either term fits in a u64, then proceed with
         * the other, so that finally we can do a u64/u64 division.
         */
        while (count_fls + sec_fls > 64 && nsec_fls + frequency_fls > 64) {
                REDUCE_FLS(nsec, frequency);
                REDUCE_FLS(sec, count);
        }

        if (count_fls + sec_fls > 64) {
                divisor = nsec * frequency;

                while (count_fls + sec_fls > 64) {
                        REDUCE_FLS(count, sec);
                        divisor >>= 1;
                }

                dividend = count * sec;
        } else {
                dividend = count * sec;

                while (nsec_fls + frequency_fls > 64) {
                        REDUCE_FLS(nsec, frequency);
                        dividend >>= 1;
                }

                divisor = nsec * frequency;
        }

        if (!divisor)
                return dividend;

        return div64_u64(dividend, divisor);
}

static void perf_event_stop(struct perf_event *event)
{
        if (!event->pmu->stop)
                return event->pmu->disable(event);

        return event->pmu->stop(event);
}

static int perf_event_start(struct perf_event *event)
{
        if (!event->pmu->start)
                return event->pmu->enable(event);

        return event->pmu->start(event);
}

static void perf_adjust_period(struct perf_event *event, u64 nsec, u64 count)
{
        struct hw_perf_event *hwc = &event->hw;
        s64 period, sample_period;
        s64 delta;

        period = perf_calculate_period(event, nsec, count);

        delta = (s64)(period - hwc->sample_period);
        delta = (delta + 7) / 8; /* low pass filter */

        sample_period = hwc->sample_period + delta;

        if (!sample_period)
                sample_period = 1;

        hwc->sample_period = sample_period;

        if (local64_read(&hwc->period_left) > 8*sample_period) {
                perf_disable();
                perf_event_stop(event);
                local64_set(&hwc->period_left, 0);
                perf_event_start(event);
                perf_enable();
        }
}

static void perf_ctx_adjust_freq(struct perf_event_context *ctx)
{
        struct perf_event *event;
        struct hw_perf_event *hwc;
        u64 interrupts, now;
        s64 delta;

        raw_spin_lock(&ctx->lock);
        list_for_each_entry_rcu(event, &ctx->event_list, event_entry) {
                if (event->state != PERF_EVENT_STATE_ACTIVE)
                        continue;

                if (event->cpu != -1 && event->cpu != smp_processor_id())
                        continue;

                hwc = &event->hw;

                interrupts = hwc->interrupts;
                hwc->interrupts = 0;

                /*
                 * unthrottle events on the tick
                 */
                if (interrupts == MAX_INTERRUPTS) {
                        perf_log_throttle(event, 1);
                        perf_disable();
                        event->pmu->unthrottle(event);
                        perf_enable();
                }

                if (!event->attr.freq || !event->attr.sample_freq)
                        continue;

                perf_disable();
                event->pmu->read(event);
                now = local64_read(&event->count);
                delta = now - hwc->freq_count_stamp;
                hwc->freq_count_stamp = now;

                if (delta > 0)
                        perf_adjust_period(event, TICK_NSEC, delta);
                perf_enable();
        }
        raw_spin_unlock(&ctx->lock);
}

/*
 * Round-robin a context's events:
 */
static void rotate_ctx(struct perf_event_context *ctx)
{
        raw_spin_lock(&ctx->lock);

        /* Rotate the first entry last of non-pinned groups */
        list_rotate_left(&ctx->flexible_groups);

        raw_spin_unlock(&ctx->lock);
}

void perf_event_task_tick(struct task_struct *curr)
{
        struct perf_cpu_context *cpuctx;
        struct perf_event_context *ctx;
        int rotate = 0;

        if (!atomic_read(&nr_events))
                return;

        cpuctx = &__get_cpu_var(perf_cpu_context);
        if (cpuctx->ctx.nr_events &&
            cpuctx->ctx.nr_events != cpuctx->ctx.nr_active)
                rotate = 1;

        ctx = curr->perf_event_ctxp;
        if (ctx && ctx->nr_events && ctx->nr_events != ctx->nr_active)
                rotate = 1;

        perf_ctx_adjust_freq(&cpuctx->ctx);
        if (ctx)
                perf_ctx_adjust_freq(ctx);

        if (!rotate)
                return;

        perf_disable();
        cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE);
        if (ctx)
                task_ctx_sched_out(ctx, EVENT_FLEXIBLE);

        rotate_ctx(&cpuctx->ctx);
        if (ctx)
                rotate_ctx(ctx);

        cpu_ctx_sched_in(cpuctx, EVENT_FLEXIBLE);
        if (ctx)
                task_ctx_sched_in(curr, EVENT_FLEXIBLE);
        perf_enable();
}

static int event_enable_on_exec(struct perf_event *event,
                                struct perf_event_context *ctx)
{
        if (!event->attr.enable_on_exec)
                return 0;

        event->attr.enable_on_exec = 0;
        if (event->state >= PERF_EVENT_STATE_INACTIVE)
                return 0;

        __perf_event_mark_enabled(event, ctx);

        return 1;
}

/*
 * Enable all of a task's events that have been marked enable-on-exec.
 * This expects task == current.
 */
static void perf_event_enable_on_exec(struct task_struct *task)
{
        struct perf_event_context *ctx;
        struct perf_event *event;
        unsigned long flags;
        int enabled = 0;
        int ret;

        local_irq_save(flags);
        ctx = task->perf_event_ctxp;
        if (!ctx || !ctx->nr_events)
                goto out;

        __perf_event_task_sched_out(ctx);

        raw_spin_lock(&ctx->lock);

        list_for_each_entry(event, &ctx->pinned_groups, group_entry) {
                ret = event_enable_on_exec(event, ctx);
                if (ret)
                        enabled = 1;
        }

        list_for_each_entry(event, &ctx->flexible_groups, group_entry) {
                ret = event_enable_on_exec(event, ctx);
                if (ret)
                        enabled = 1;
        }

        /*
         * Unclone this context if we enabled any event.
         */
        if (enabled)
                unclone_ctx(ctx);

        raw_spin_unlock(&ctx->lock);

        perf_event_task_sched_in(task);
 out:
        local_irq_restore(flags);
}

/*
 * Cross CPU call to read the hardware event
 */
static void __perf_event_read(void *info)
{
        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
        struct perf_event *event = info;
        struct perf_event_context *ctx = event->ctx;

        /*
         * If this is a task context, we need to check whether it is
         * the current task context of this cpu.  If not it has been
         * scheduled out before the smp call arrived.  In that case
         * event->count would have been updated to a recent sample
         * when the event was scheduled out.
         */
        if (ctx->task && cpuctx->task_ctx != ctx)
                return;

        raw_spin_lock(&ctx->lock);
        update_context_time(ctx);
        update_event_times(event);
        raw_spin_unlock(&ctx->lock);

        event->pmu->read(event);
}

static inline u64 perf_event_count(struct perf_event *event)
{
        return local64_read(&event->count) + atomic64_read(&event->child_count);
}

static u64 perf_event_read(struct perf_event *event)
{
        /*
         * If event is enabled and currently active on a CPU, update the
         * value in the event structure:
         */
        if (event->state == PERF_EVENT_STATE_ACTIVE) {
                smp_call_function_single(event->oncpu,
                                         __perf_event_read, event, 1);
        } else if (event->state == PERF_EVENT_STATE_INACTIVE) {
                struct perf_event_context *ctx = event->ctx;
                unsigned long flags;

                raw_spin_lock_irqsave(&ctx->lock, flags);
                update_context_time(ctx);
                update_event_times(event);
                raw_spin_unlock_irqrestore(&ctx->lock, flags);
        }

        return perf_event_count(event);
}

/*
 * Initialize the perf_event context in a task_struct:
 */
static void
__perf_event_init_context(struct perf_event_context *ctx,
                            struct task_struct *task)
{
        raw_spin_lock_init(&ctx->lock);
        mutex_init(&ctx->mutex);
        INIT_LIST_HEAD(&ctx->pinned_groups);
        INIT_LIST_HEAD(&ctx->flexible_groups);
        INIT_LIST_HEAD(&ctx->event_list);
        atomic_set(&ctx->refcount, 1);
        ctx->task = task;
}

static struct perf_event_context *find_get_context(pid_t pid, int cpu)
{
        struct perf_event_context *ctx;
        struct perf_cpu_context *cpuctx;
        struct task_struct *task;
        unsigned long flags;
        int err;

        if (pid == -1 && cpu != -1) {
                /* Must be root to operate on a CPU event: */
                if (perf_paranoid_cpu() && !capable(CAP_SYS_ADMIN))
                        return ERR_PTR(-EACCES);

                if (cpu < 0 || cpu >= nr_cpumask_bits)
                        return ERR_PTR(-EINVAL);

                /*
                 * We could be clever and allow to attach a event to an
                 * offline CPU and activate it when the CPU comes up, but
                 * that's for later.
                 */
                if (!cpu_online(cpu))
                        return ERR_PTR(-ENODEV);

                cpuctx = &per_cpu(perf_cpu_context, cpu);
                ctx = &cpuctx->ctx;
                get_ctx(ctx);

                return ctx;
        }

        rcu_read_lock();
        if (!pid)
                task = current;
        else
                task = find_task_by_vpid(pid);
        if (task)
                get_task_struct(task);
        rcu_read_unlock();

        if (!task)
                return ERR_PTR(-ESRCH);

        /*
         * Can't attach events to a dying task.
         */
        err = -ESRCH;
        if (task->flags & PF_EXITING)
                goto errout;

        /* Reuse ptrace permission checks for now. */
        err = -EACCES;
        if (!ptrace_may_access(task, PTRACE_MODE_READ))
                goto errout;

 retry:
        ctx = perf_lock_task_context(task, &flags);
        if (ctx) {
                unclone_ctx(ctx);
                raw_spin_unlock_irqrestore(&ctx->lock, flags);
        }

        if (!ctx) {
                ctx = kzalloc(sizeof(struct perf_event_context), GFP_KERNEL);
                err = -ENOMEM;
                if (!ctx)
                        goto errout;
                __perf_event_init_context(ctx, task);
                get_ctx(ctx);
                if (cmpxchg(&task->perf_event_ctxp, NULL, ctx)) {
                        /*
                         * We raced with some other task; use
                         * the context they set.
                         */
                        kfree(ctx);
                        goto retry;
                }
                get_task_struct(task);
        }

        put_task_struct(task);
        return ctx;

 errout:
        put_task_struct(task);
        return ERR_PTR(err);
}

static void perf_event_free_filter(struct perf_event *event);

static void free_event_rcu(struct rcu_head *head)
{
        struct perf_event *event;

        event = container_of(head, struct perf_event, rcu_head);
        if (event->ns)
                put_pid_ns(event->ns);
        perf_event_free_filter(event);
        kfree(event);
}

static void perf_pending_sync(struct perf_event *event);
static void perf_buffer_put(struct perf_buffer *buffer);

static void free_event(struct perf_event *event)
{
        perf_pending_sync(event);

        if (!event->parent) {
                atomic_dec(&nr_events);
                if (event->attr.mmap || event->attr.mmap_data)
                        atomic_dec(&nr_mmap_events);
                if (event->attr.comm)
                        atomic_dec(&nr_comm_events);
                if (event->attr.task)
                        atomic_dec(&nr_task_events);
        }

        if (event->buffer) {
                perf_buffer_put(event->buffer);
                event->buffer = NULL;
        }

        if (event->destroy)
                event->destroy(event);

        put_ctx(event->ctx);
        call_rcu(&event->rcu_head, free_event_rcu);
}

int perf_event_release_kernel(struct perf_event *event)
{
        struct perf_event_context *ctx = event->ctx;

        /*
         * Remove from the PMU, can't get re-enabled since we got
         * here because the last ref went.
         */
        perf_event_disable(event);

        WARN_ON_ONCE(ctx->parent_ctx);
        /*
         * There are two ways this annotation is useful:
         *
         *  1) there is a lock recursion from perf_event_exit_task
         *     see the comment there.
         *
         *  2) there is a lock-inversion with mmap_sem through
         *     perf_event_read_group(), which takes faults while
         *     holding ctx->mutex, however this is called after
         *     the last filedesc died, so there is no possibility
         *     to trigger the AB-BA case.
         */
        mutex_lock_nested(&ctx->mutex, SINGLE_DEPTH_NESTING);
        raw_spin_lock_irq(&ctx->lock);
        perf_group_detach(event);
        list_del_event(event, ctx);
        raw_spin_unlock_irq(&ctx->lock);
        mutex_unlock(&ctx->mutex);

        mutex_lock(&event->owner->perf_event_mutex);
        list_del_init(&event->owner_entry);
        mutex_unlock(&event->owner->perf_event_mutex);
        put_task_struct(event->owner);

        free_event(event);

        return 0;
}
EXPORT_SYMBOL_GPL(perf_event_release_kernel);

/*
 * Called when the last reference to the file is gone.
 */
static int perf_release(struct inode *inode, struct file *file)
{
        struct perf_event *event = file->private_data;

        file->private_data = NULL;

        return perf_event_release_kernel(event);
}

static int perf_event_read_size(struct perf_event *event)
{
        int entry = sizeof(u64); /* value */
        int size = 0;
        int nr = 1;

        if (event->attr.read_format & PERF_FORMAT_TOTAL_TIME_ENABLED)
                size += sizeof(u64);

        if (event->attr.read_format & PERF_FORMAT_TOTAL_TIME_RUNNING)
                size += sizeof(u64);

        if (event->attr.read_format & PERF_FORMAT_ID)
                entry += sizeof(u64);

        if (event->attr.read_format & PERF_FORMAT_GROUP) {
                nr += event->group_leader->nr_siblings;
                size += sizeof(u64);
        }

        size += entry * nr;

        return size;
}

u64 perf_event_read_value(struct perf_event *event, u64 *enabled, u64 *running)
{
        struct perf_event *child;
        u64 total = 0;

        *enabled = 0;
        *running = 0;

        mutex_lock(&event->child_mutex);
        total += perf_event_read(event);
        *enabled += event->total_time_enabled +
                        atomic64_read(&event->child_total_time_enabled);
        *running += event->total_time_running +
                        atomic64_read(&event->child_total_time_running);

        list_for_each_entry(child, &event->child_list, child_list) {
                total += perf_event_read(child);
                *enabled += child->total_time_enabled;
                *running += child->total_time_running;
        }
        mutex_unlock(&event->child_mutex);

        return total;
}
EXPORT_SYMBOL_GPL(perf_event_read_value);

static int perf_event_read_group(struct perf_event *event,
                                   u64 read_format, char __user *buf)
{
        struct perf_event *leader = event->group_leader, *sub;
        int n = 0, size = 0, ret = -EFAULT;
        struct perf_event_context *ctx = leader->ctx;
        u64 values[5];
        u64 count, enabled, running;

        mutex_lock(&ctx->mutex);
        count = perf_event_read_value(leader, &enabled, &running);

        values[n++] = 1 + leader->nr_siblings;
        if (read_format & PERF_FORMAT_TOTAL_TIME_ENABLED)
                values[n++] = enabled;
        if (read_format & PERF_FORMAT_TOTAL_TIME_RUNNING)
                values[n++] = running;
        values[n++] = count;
        if (read_format & PERF_FORMAT_ID)
                values[n++] = primary_event_id(leader);

        size = n * sizeof(u64);

        if (copy_to_user(buf, values, size))
                goto unlock;

        ret = size;

        list_for_each_entry(sub, &leader->sibling_list, group_entry) {
                n = 0;

                values[n++] = perf_event_read_value(sub, &enabled, &running);
                if (read_format & PERF_FORMAT_ID)
                        values[n++] = primary_event_id(sub);

                size = n * sizeof(u64);

                if (copy_to_user(buf + ret, values, size)) {
                        ret = -EFAULT;
                        goto unlock;
                }

                ret += size;
        }
unlock:
        mutex_unlock(&ctx->mutex);

        return ret;
}

static int perf_event_read_one(struct perf_event *event,
                                 u64 read_format, char __user *buf)
{
        u64 enabled, running;
        u64 values[4];
        int n = 0;

        values[n++] = perf_event_read_value(event, &enabled, &running);
        if (read_format & PERF_FORMAT_TOTAL_TIME_ENABLED)
                values[n++] = enabled;
        if (read_format & PERF_FORMAT_TOTAL_TIME_RUNNING)
                values[n++] = running;
        if (read_format & PERF_FORMAT_ID)
                values[n++] = primary_event_id(event);

        if (copy_to_user(buf, values, n * sizeof(u64)))
                return -EFAULT;

        return n * sizeof(u64);
}

/*
 * Read the performance event - simple non blocking version for now
 */
static ssize_t
perf_read_hw(struct perf_event *event, char __user *buf, size_t count)
{
        u64 read_format = event->attr.read_format;
        int ret;

        /*
         * Return end-of-file for a read on a event that is in
         * error state (i.e. because it was pinned but it couldn't be
         * scheduled on to the CPU at some point).
         */
        if (event->state == PERF_EVENT_STATE_ERROR)
                return 0;

        if (count < perf_event_read_size(event))
                return -ENOSPC;

        WARN_ON_ONCE(event->ctx->parent_ctx);
        if (read_format & PERF_FORMAT_GROUP)
                ret = perf_event_read_group(event, read_format, buf);
        else
                ret = perf_event_read_one(event, read_format, buf);

        return ret;
}

static ssize_t
perf_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
{
        struct perf_event *event = file->private_data;

        return perf_read_hw(event, buf, count);
}

static unsigned int perf_poll(struct file *file, poll_table *wait)
{
        struct perf_event *event = file->private_data;
        struct perf_buffer *buffer;
        unsigned int events = POLL_HUP;

        rcu_read_lock();
        buffer = rcu_dereference(event->buffer);
        if (buffer)
                events = atomic_xchg(&buffer->poll, 0);
        rcu_read_unlock();

        poll_wait(file, &event->waitq, wait);

        return events;
}

static void perf_event_reset(struct perf_event *event)
{
        (void)perf_event_read(event);
        local64_set(&event->count, 0);
        perf_event_update_userpage(event);
}

/*
 * Holding the top-level event's child_mutex means that any
 * descendant process that has inherited this event will block
 * in sync_child_event if it goes to exit, thus satisfying the
 * task existence requirements of perf_event_enable/disable.
 */
static void perf_event_for_each_child(struct perf_event *event,
                                        void (*func)(struct perf_event *))
{
        struct perf_event *child;

        WARN_ON_ONCE(event->ctx->parent_ctx);
        mutex_lock(&event->child_mutex);
        func(event);
        list_for_each_entry(child, &event->child_list, child_list)
                func(child);
        mutex_unlock(&event->child_mutex);
}

static void perf_event_for_each(struct perf_event *event,
                                  void (*func)(struct perf_event *))
{
        struct perf_event_context *ctx = event->ctx;
        struct perf_event *sibling;

        WARN_ON_ONCE(ctx->parent_ctx);
        mutex_lock(&ctx->mutex);
        event = event->group_leader;

        perf_event_for_each_child(event, func);
        func(event);
        list_for_each_entry(sibling, &event->sibling_list, group_entry)
                perf_event_for_each_child(event, func);
        mutex_unlock(&ctx->mutex);
}

static int perf_event_period(struct perf_event *event, u64 __user *arg)
{
        struct perf_event_context *ctx = event->ctx;
        int ret = 0;
        u64 value;

        if (!event->attr.sample_period)
                return -EINVAL;

        if (copy_from_user(&value, arg, sizeof(value)))
                return -EFAULT;

        if (!value)
                return -EINVAL;

        raw_spin_lock_irq(&ctx->lock);
        if (event->attr.freq) {
                if (value > sysctl_perf_event_sample_rate) {
                        ret = -EINVAL;
                        goto unlock;
                }

                event->attr.sample_freq = value;
        } else {
                event->attr.sample_period = value;
                event->hw.sample_period = value;
        }
unlock:
        raw_spin_unlock_irq(&ctx->lock);

        return ret;
}

static const struct file_operations perf_fops;

static struct perf_event *perf_fget_light(int fd, int *fput_needed)
{
        struct file *file;

        file = fget_light(fd, fput_needed);
        if (!file)
                return ERR_PTR(-EBADF);

        if (file->f_op != &perf_fops) {
                fput_light(file, *fput_needed);
                *fput_needed = 0;
                return ERR_PTR(-EBADF);
        }

        return file->private_data;
}

static int perf_event_set_output(struct perf_event *event,
                                 struct perf_event *output_event);
static int perf_event_set_filter(struct perf_event *event, void __user *arg);

static long perf_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
        struct perf_event *event = file->private_data;
        void (*func)(struct perf_event *);
        u32 flags = arg;

        switch (cmd) {
        case PERF_EVENT_IOC_ENABLE:
                func = perf_event_enable;
                break;
        case PERF_EVENT_IOC_DISABLE:
                func = perf_event_disable;
                break;
        case PERF_EVENT_IOC_RESET:
                func = perf_event_reset;
                break;

        case PERF_EVENT_IOC_REFRESH:
                return perf_event_refresh(event, arg);

        case PERF_EVENT_IOC_PERIOD:
                return perf_event_period(event, (u64 __user *)arg);

        case PERF_EVENT_IOC_SET_OUTPUT:
        {
                struct perf_event *output_event = NULL;
                int fput_needed = 0;
                int ret;

                if (arg != -1) {
                        output_event = perf_fget_light(arg, &fput_needed);
                        if (IS_ERR(output_event))
                                return PTR_ERR(output_event);
                }

                ret = perf_event_set_output(event, output_event);
                if (output_event)
                        fput_light(output_event->filp, fput_needed);

                return ret;
        }

        case PERF_EVENT_IOC_SET_FILTER:
                return perf_event_set_filter(event, (void __user *)arg);

        default:
                return -ENOTTY;
        }

        if (flags & PERF_IOC_FLAG_GROUP)
                perf_event_for_each(event, func);
        else
                perf_event_for_each_child(event, func);

        return 0;
}

int perf_event_task_enable(void)
{
        struct perf_event *event;

        mutex_lock(&current->perf_event_mutex);
        list_for_each_entry(event, &current->perf_event_list, owner_entry)
                perf_event_for_each_child(event, perf_event_enable);
        mutex_unlock(&current->perf_event_mutex);

        return 0;
}

int perf_event_task_disable(void)
{
        struct perf_event *event;

        mutex_lock(&current->perf_event_mutex);
        list_for_each_entry(event, &current->perf_event_list, owner_entry)
                perf_event_for_each_child(event, perf_event_disable);
        mutex_unlock(&current->perf_event_mutex);

        return 0;
}

#ifndef PERF_EVENT_INDEX_OFFSET
# define PERF_EVENT_INDEX_OFFSET 0
#endif

static int perf_event_index(struct perf_event *event)
{
        if (event->state != PERF_EVENT_STATE_ACTIVE)
                return 0;

        return event->hw.idx + 1 - PERF_EVENT_INDEX_OFFSET;
}

/*
 * Callers need to ensure there can be no nesting of this function, otherwise
 * the seqlock logic goes bad. We can not serialize this because the arch
 * code calls this from NMI context.
 */
void perf_event_update_userpage(struct perf_event *event)
{
        struct perf_event_mmap_page *userpg;
        struct perf_buffer *buffer;

        rcu_read_lock();
        buffer = rcu_dereference(event->buffer);
        if (!buffer)
                goto unlock;

        userpg = buffer->user_page;

        /*
         * Disable preemption so as to not let the corresponding user-space
         * spin too long if we get preempted.
         */
        preempt_disable();
        ++userpg->lock;
        barrier();
        userpg->index = perf_event_index(event);
        userpg->offset = perf_event_count(event);
        if (event->state == PERF_EVENT_STATE_ACTIVE)
                userpg->offset -= local64_read(&event->hw.prev_count);

        userpg->time_enabled = event->total_time_enabled +
                        atomic64_read(&event->child_total_time_enabled);

        userpg->time_running = event->total_time_running +
                        atomic64_read(&event->child_total_time_running);

        barrier();
        ++userpg->lock;
        preempt_enable();
unlock:
        rcu_read_unlock();
}

static unsigned long perf_data_size(struct perf_buffer *buffer);

static void
perf_buffer_init(struct perf_buffer *buffer, long watermark, int flags)
{
        long max_size = perf_data_size(buffer);

        if (watermark)
                buffer->watermark = min(max_size, watermark);

        if (!buffer->watermark)
                buffer->watermark = max_size / 2;

        if (flags & PERF_BUFFER_WRITABLE)
                buffer->writable = 1;

        atomic_set(&buffer->refcount, 1);
}

#ifndef CONFIG_PERF_USE_VMALLOC

/*
 * Back perf_mmap() with regular GFP_KERNEL-0 pages.
 */

static struct page *
perf_mmap_to_page(struct perf_buffer *buffer, unsigned long pgoff)
{
        if (pgoff > buffer->nr_pages)
                return NULL;

        if (pgoff == 0)
                return virt_to_page(buffer->user_page);

        return virt_to_page(buffer->data_pages[pgoff - 1]);
}

static void *perf_mmap_alloc_page(int cpu)
{
        struct page *page;
        int node;

        node = (cpu == -1) ? cpu : cpu_to_node(cpu);
        page = alloc_pages_node(node, GFP_KERNEL | __GFP_ZERO, 0);
        if (!page)
                return NULL;

        return page_address(page);
}

static struct perf_buffer *
perf_buffer_alloc(int nr_pages, long watermark, int cpu, int flags)
{
        struct perf_buffer *buffer;
        unsigned long size;
        int i;

        size = sizeof(struct perf_buffer);
        size += nr_pages * sizeof(void *);

        buffer = kzalloc(size, GFP_KERNEL);
        if (!buffer)
                goto fail;

        buffer->user_page = perf_mmap_alloc_page(cpu);
        if (!buffer->user_page)
                goto fail_user_page;

        for (i = 0; i < nr_pages; i++) {
                buffer->data_pages[i] = perf_mmap_alloc_page(cpu);
                if (!buffer->data_pages[i])
                        goto fail_data_pages;
        }

        buffer->nr_pages = nr_pages;

        perf_buffer_init(buffer, watermark, flags);

        return buffer;

fail_data_pages:
        for (i--; i >= 0; i--)
                free_page((unsigned long)buffer->data_pages[i]);

        free_page((unsigned long)buffer->user_page);

fail_user_page:
        kfree(buffer);

fail:
        return NULL;
}

static void perf_mmap_free_page(unsigned long addr)
{
        struct page *page = virt_to_page((void *)addr);

        page->mapping = NULL;
        __free_page(page);
}

static void perf_buffer_free(struct perf_buffer *buffer)
{
        int i;

        perf_mmap_free_page((unsigned long)buffer->user_page);
        for (i = 0; i < buffer->nr_pages; i++)
                perf_mmap_free_page((unsigned long)buffer->data_pages[i]);
        kfree(buffer);
}

static inline int page_order(struct perf_buffer *buffer)
{
        return 0;
}

#else

/*
 * Back perf_mmap() with vmalloc memory.
 *
 * Required for architectures that have d-cache aliasing issues.
 */

static inline int page_order(struct perf_buffer *buffer)
{
        return buffer->page_order;
}

static struct page *
perf_mmap_to_page(struct perf_buffer *buffer, unsigned long pgoff)
{
        if (pgoff > (1UL << page_order(buffer)))
                return NULL;

        return vmalloc_to_page((void *)buffer->user_page + pgoff * PAGE_SIZE);
}

static void perf_mmap_unmark_page(void *addr)
{
        struct page *page = vmalloc_to_page(addr);

        page->mapping = NULL;
}

static void perf_buffer_free_work(struct work_struct *work)
{
        struct perf_buffer *buffer;
        void *base;
        int i, nr;

        buffer = container_of(work, struct perf_buffer, work);
        nr = 1 << page_order(buffer);

        base = buffer->user_page;
        for (i = 0; i < nr + 1; i++)
                perf_mmap_unmark_page(base + (i * PAGE_SIZE));

        vfree(base);
        kfree(buffer);
}

static void perf_buffer_free(struct perf_buffer *buffer)
{
        schedule_work(&buffer->work);
}

static struct perf_buffer *
perf_buffer_alloc(int nr_pages, long watermark, int cpu, int flags)
{
        struct perf_buffer *buffer;
        unsigned long size;
        void *all_buf;

        size = sizeof(struct perf_buffer);
        size += sizeof(void *);

        buffer = kzalloc(size, GFP_KERNEL);
        if (!buffer)
                goto fail;

        INIT_WORK(&buffer->work, perf_buffer_free_work);

        all_buf = vmalloc_user((nr_pages + 1) * PAGE_SIZE);
        if (!all_buf)
                goto fail_all_buf;

        buffer->user_page = all_buf;
        buffer->data_pages[0] = all_buf + PAGE_SIZE;
        buffer->page_order = ilog2(nr_pages);
        buffer->nr_pages = 1;

        perf_buffer_init(buffer, watermark, flags);

        return buffer;

fail_all_buf:
        kfree(buffer);

fail:
        return NULL;
}

#endif

static unsigned long perf_data_size(struct perf_buffer *buffer)
{
        return buffer->nr_pages << (PAGE_SHIFT + page_order(buffer));
}

static int perf_mmap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
{
        struct perf_event *event = vma->vm_file->private_data;
        struct perf_buffer *buffer;
        int ret = VM_FAULT_SIGBUS;

        if (vmf->flags & FAULT_FLAG_MKWRITE) {
                if (vmf->pgoff == 0)
                        ret = 0;
                return ret;
        }

        rcu_read_lock();
        buffer = rcu_dereference(event->buffer);
        if (!buffer)
                goto unlock;

        if (vmf->pgoff && (vmf->flags & FAULT_FLAG_WRITE))
                goto unlock;

        vmf->page = perf_mmap_to_page(buffer, vmf->pgoff);
        if (!vmf->page)
                goto unlock;

        get_page(vmf->page);
        vmf->page->mapping = vma->vm_file->f_mapping;
        vmf->page->index   = vmf->pgoff;

        ret = 0;
unlock:
        rcu_read_unlock();

        return ret;
}

static void perf_buffer_free_rcu(struct rcu_head *rcu_head)
{
        struct perf_buffer *buffer;

        buffer = container_of(rcu_head, struct perf_buffer, rcu_head);
        perf_buffer_free(buffer);
}

static struct perf_buffer *perf_buffer_get(struct perf_event *event)
{
        struct perf_buffer *buffer;

        rcu_read_lock();
        buffer = rcu_dereference(event->buffer);
        if (buffer) {
                if (!atomic_inc_not_zero(&buffer->refcount))
                        buffer = NULL;
        }
        rcu_read_unlock();

        return buffer;
}

static void perf_buffer_put(struct perf_buffer *buffer)
{
        if (!atomic_dec_and_test(&buffer->refcount))
                return;

        call_rcu(&buffer->rcu_head, perf_buffer_free_rcu);
}

static void perf_mmap_open(struct vm_area_struct *vma)
{
        struct perf_event *event = vma->vm_file->private_data;

        atomic_inc(&event->mmap_count);
}

static void perf_mmap_close(struct vm_area_struct *vma)
{
        struct perf_event *event = vma->vm_file->private_data;

        if (atomic_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex)) {
                unsigned long size = perf_data_size(event->buffer);
                struct user_struct *user = event->mmap_user;
                struct perf_buffer *buffer = event->buffer;

                atomic_long_sub((size >> PAGE_SHIFT) + 1, &user->locked_vm);
                vma->vm_mm->locked_vm -= event->mmap_locked;
                rcu_assign_pointer(event->buffer, NULL);
                mutex_unlock(&event->mmap_mutex);

                perf_buffer_put(buffer);
                free_uid(user);
        }
}

static const struct vm_operations_struct perf_mmap_vmops = {
        .open           = perf_mmap_open,
        .close          = perf_mmap_close,
        .fault          = perf_mmap_fault,
        .page_mkwrite   = perf_mmap_fault,
};

static int perf_mmap(struct file *file, struct vm_area_struct *vma)
{
        struct perf_event *event = file->private_data;
        unsigned long user_locked, user_lock_limit;
        struct user_struct *user = current_user();
        unsigned long locked, lock_limit;
        struct perf_buffer *buffer;
        unsigned long vma_size;
        unsigned long nr_pages;
        long user_extra, extra;
        int ret = 0, flags = 0;

        /*
         * Don't allow mmap() of inherited per-task counters. This would
         * create a performance issue due to all children writing to the
         * same buffer.
         */
        if (event->cpu == -1 && event->attr.inherit)
                return -EINVAL;

        if (!(vma->vm_flags & VM_SHARED))
                return -EINVAL;

        vma_size = vma->vm_end - vma->vm_start;
        nr_pages = (vma_size / PAGE_SIZE) - 1;

        /*
         * If we have buffer pages ensure they're a power-of-two number, so we
         * can do bitmasks instead of modulo.
         */
        if (nr_pages != 0 && !is_power_of_2(nr_pages))
                return -EINVAL;

        if (vma_size != PAGE_SIZE * (1 + nr_pages))
                return -EINVAL;

        if (vma->vm_pgoff != 0)
                return -EINVAL;

        WARN_ON_ONCE(event->ctx->parent_ctx);
        mutex_lock(&event->mmap_mutex);
        if (event->buffer) {
                if (event->buffer->nr_pages == nr_pages)
                        atomic_inc(&event->buffer->refcount);
                else
                        ret = -EINVAL;
                goto unlock;
        }

        user_extra = nr_pages + 1;
        user_lock_limit = sysctl_perf_event_mlock >> (PAGE_SHIFT - 10);

        /*
         * Increase the limit linearly with more CPUs:
         */
        user_lock_limit *= num_online_cpus();

        user_locked = atomic_long_read(&user->locked_vm) + user_extra;

        extra = 0;
        if (user_locked > user_lock_limit)
                extra = user_locked - user_lock_limit;

        lock_limit = rlimit(RLIMIT_MEMLOCK);
        lock_limit >>= PAGE_SHIFT;
        locked = vma->vm_mm->locked_vm + extra;

        if ((locked > lock_limit) && perf_paranoid_tracepoint_raw() &&
                !capable(CAP_IPC_LOCK)) {
                ret = -EPERM;
                goto unlock;
        }

        WARN_ON(event->buffer);

        if (vma->vm_flags & VM_WRITE)
                flags |= PERF_BUFFER_WRITABLE;

        buffer = perf_buffer_alloc(nr_pages, event->attr.wakeup_watermark,
                                   event->cpu, flags);
        if (!buffer) {
                ret = -ENOMEM;
                goto unlock;
        }
        rcu_assign_pointer(event->buffer, buffer);

        atomic_long_add(user_extra, &user->locked_vm);
        event->mmap_locked = extra;
        event->mmap_user = get_current_user();
        vma->vm_mm->locked_vm += event->mmap_locked;

unlock:
        if (!ret)
                atomic_inc(&event->mmap_count);
        mutex_unlock(&event->mmap_mutex);

        vma->vm_flags |= VM_RESERVED;
        vma->vm_ops = &perf_mmap_vmops;

        return ret;
}

static int perf_fasync(int fd, struct file *filp, int on)
{
        struct inode *inode = filp->f_path.dentry->d_inode;
        struct perf_event *event = filp->private_data;
        int retval;

        mutex_lock(&inode->i_mutex);
        retval = fasync_helper(fd, filp, on, &event->fasync);
        mutex_unlock(&inode->i_mutex);

        if (retval < 0)
                return retval;

        return 0;
}

static const struct file_operations perf_fops = {
        .llseek                 = no_llseek,
        .release                = perf_release,
        .read                   = perf_read,
        .poll                   = perf_poll,
        .unlocked_ioctl         = perf_ioctl,
        .compat_ioctl           = perf_ioctl,
        .mmap                   = perf_mmap,
        .fasync                 = perf_fasync,
};

/*
 * Perf event wakeup
 *
 * If there's data, ensure we set the poll() state and publish everything
 * to user-space before waking everybody up.
 */

void perf_event_wakeup(struct perf_event *event)
{
        wake_up_all(&event->waitq);

        if (event->pending_kill) {
                kill_fasync(&event->fasync, SIGIO, event->pending_kill);
                event->pending_kill = 0;
        }
}

/*
 * Pending wakeups
 *
 * Handle the case where we need to wakeup up from NMI (or rq->lock) context.
 *
 * The NMI bit means we cannot possibly take locks. Therefore, maintain a
 * single linked list and use cmpxchg() to add entries lockless.
 */

static void perf_pending_event(struct perf_pending_entry *entry)
{
        struct perf_event *event = container_of(entry,
                        struct perf_event, pending);

        if (event->pending_disable) {
                event->pending_disable = 0;
                __perf_event_disable(event);
        }

        if (event->pending_wakeup) {
                event->pending_wakeup = 0;
                perf_event_wakeup(event);
        }
}

#define PENDING_TAIL ((struct perf_pending_entry *)-1UL)

static DEFINE_PER_CPU(struct perf_pending_entry *, perf_pending_head) = {
        PENDING_TAIL,
};

static void perf_pending_queue(struct perf_pending_entry *entry,
                               void (*func)(struct perf_pending_entry *))
{
        struct perf_pending_entry **head;

        if (cmpxchg(&entry->next, NULL, PENDING_TAIL) != NULL)
                return;

        entry->func = func;

        head = &get_cpu_var(perf_pending_head);

        do {
                entry->next = *head;
        } while (cmpxchg(head, entry->next, entry) != entry->next);

        set_perf_event_pending();

        put_cpu_var(perf_pending_head);
}

static int __perf_pending_run(void)
{
        struct perf_pending_entry *list;
        int nr = 0;

        list = xchg(&__get_cpu_var(perf_pending_head), PENDING_TAIL);
        while (list != PENDING_TAIL) {
                void (*func)(struct perf_pending_entry *);
                struct perf_pending_entry *entry = list;

                list = list->next;

                func = entry->func;
                entry->next = NULL;
                /*
                 * Ensure we observe the unqueue before we issue the wakeup,
                 * so that we won't be waiting forever.
                 * -- see perf_not_pending().
                 */
                smp_wmb();

                func(entry);
                nr++;
        }

        return nr;
}

static inline int perf_not_pending(struct perf_event *event)
{
        /*
         * If we flush on whatever cpu we run, there is a chance we don't
         * need to wait.
         */
        get_cpu();
        __perf_pending_run();
        put_cpu();

        /*
         * Ensure we see the proper queue state before going to sleep
         * so that we do not miss the wakeup. -- see perf_pending_handle()
         */
        smp_rmb();
        return event->pending.next == NULL;
}

static void perf_pending_sync(struct perf_event *event)
{
        wait_event(event->waitq, perf_not_pending(event));
}

void perf_event_do_pending(void)
{
        __perf_pending_run();
}

/*
 * Callchain support -- arch specific
 */

__weak struct perf_callchain_entry *perf_callchain(struct pt_regs *regs)
{
        return NULL;
}


/*
 * We assume there is only KVM supporting the callbacks.
 * Later on, we might change it to a list if there is
 * another virtualization implementation supporting the callbacks.
 */
struct perf_guest_info_callbacks *perf_guest_cbs;

int perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
{
        perf_guest_cbs = cbs;
        return 0;
}
EXPORT_SYMBOL_GPL(perf_register_guest_info_callbacks);

int perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
{
        perf_guest_cbs = NULL;
        return 0;
}
EXPORT_SYMBOL_GPL(perf_unregister_guest_info_callbacks);

/*
 * Output
 */
static bool perf_output_space(struct perf_buffer *buffer, unsigned long tail,
                              unsigned long offset, unsigned long head)
{
        unsigned long mask;

        if (!buffer->writable)
                return true;

        mask = perf_data_size(buffer) - 1;

        offset = (offset - tail) & mask;
        head   = (head   - tail) & mask;

        if ((int)(head - offset) < 0)
                return false;

        return true;
}

static void perf_output_wakeup(struct perf_output_handle *handle)
{
        atomic_set(&handle->buffer->poll, POLL_IN);

        if (handle->nmi) {
                handle->event->pending_wakeup = 1;
                perf_pending_queue(&handle->event->pending,
                                   perf_pending_event);
        } else
                perf_event_wakeup(handle->event);
}

/*
 * We need to ensure a later event_id doesn't publish a head when a former
 * event isn't done writing. However since we need to deal with NMIs we
 * cannot fully serialize things.
 *
 * We only publish the head (and generate a wakeup) when the outer-most
 * event completes.
 */
static void perf_output_get_handle(struct perf_output_handle *handle)
{
        struct perf_buffer *buffer = handle->buffer;

        preempt_disable();
        local_inc(&buffer->nest);
        handle->wakeup = local_read(&buffer->wakeup);
}

static void perf_output_put_handle(struct perf_output_handle *handle)
{
        struct perf_buffer *buffer = handle->buffer;
        unsigned long head;

again:
        head = local_read(&buffer->head);

        /*
         * IRQ/NMI can happen here, which means we can miss a head update.
         */

        if (!local_dec_and_test(&buffer->nest))
                goto out;

        /*
         * Publish the known good head. Rely on the full barrier implied
         * by atomic_dec_and_test() order the buffer->head read and this
         * write.
         */
        buffer->user_page->data_head = head;

        /*
         * Now check if we missed an update, rely on the (compiler)
         * barrier in atomic_dec_and_test() to re-read buffer->head.
         */
        if (unlikely(head != local_read(&buffer->head))) {
                local_inc(&buffer->nest);
                goto again;
        }

        if (handle->wakeup != local_read(&buffer->wakeup))
                perf_output_wakeup(handle);

 out:
        preempt_enable();
}

__always_inline void perf_output_copy(struct perf_output_handle *handle,
                      const void *buf, unsigned int len)
{
        do {
                unsigned long size = min_t(unsigned long, handle->size, len);

                memcpy(handle->addr, buf, size);

                len -= size;
                handle->addr += size;
                buf += size;
                handle->size -= size;
                if (!handle->size) {
                        struct perf_buffer *buffer = handle->buffer;

                        handle->page++;
                        handle->page &= buffer->nr_pages - 1;
                        handle->addr = buffer->data_pages[handle->page];
                        handle->size = PAGE_SIZE << page_order(buffer);
                }
        } while (len);
}

int perf_output_begin(struct perf_output_handle *handle,
                      struct perf_event *event, unsigned int size,
                      int nmi, int sample)
{
        struct perf_buffer *buffer;
        unsigned long tail, offset, head;
        int have_lost;
        struct {
                struct perf_event_header header;
                u64                      id;
                u64                      lost;
        } lost_event;

        rcu_read_lock();
        /*
         * For inherited events we send all the output towards the parent.
         */
        if (event->parent)
                event = event->parent;

        buffer = rcu_dereference(event->buffer);
        if (!buffer)
                goto out;

        handle->buffer  = buffer;
        handle->event   = event;
        handle->nmi     = nmi;
        handle->sample  = sample;

        if (!buffer->nr_pages)
                goto out;

        have_lost = local_read(&buffer->lost);
        if (have_lost)
                size += sizeof(lost_event);

        perf_output_get_handle(handle);

        do {
                /*
                 * Userspace could choose to issue a mb() before updating the
                 * tail pointer. So that all reads will be completed before the
                 * write is issued.
                 */
                tail = ACCESS_ONCE(buffer->user_page->data_tail);
                smp_rmb();
                offset = head = local_read(&buffer->head);
                head += size;
                if (unlikely(!perf_output_space(buffer, tail, offset, head)))
                        goto fail;
        } while (local_cmpxchg(&buffer->head, offset, head) != offset);

        if (head - local_read(&buffer->wakeup) > buffer->watermark)
                local_add(buffer->watermark, &buffer->wakeup);

        handle->page = offset >> (PAGE_SHIFT + page_order(buffer));
        handle->page &= buffer->nr_pages - 1;
        handle->size = offset & ((PAGE_SIZE << page_order(buffer)) - 1);
        handle->addr = buffer->data_pages[handle->page];
        handle->addr += handle->size;
        handle->size = (PAGE_SIZE << page_order(buffer)) - handle->size;

        if (have_lost) {
                lost_event.header.type = PERF_RECORD_LOST;
                lost_event.header.misc = 0;
                lost_event.header.size = sizeof(lost_event);
                lost_event.id          = event->id;
                lost_event.lost        = local_xchg(&buffer->lost, 0);

                perf_output_put(handle, lost_event);
        }

        return 0;

fail:
        local_inc(&buffer->lost);
        perf_output_put_handle(handle);
out:
        rcu_read_unlock();

        return -ENOSPC;
}

void perf_output_end(struct perf_output_handle *handle)
{
        struct perf_event *event = handle->event;
        struct perf_buffer *buffer = handle->buffer;

        int wakeup_events = event->attr.wakeup_events;

        if (handle->sample && wakeup_events) {
                int events = local_inc_return(&buffer->events);
                if (events >= wakeup_events) {
                        local_sub(wakeup_events, &buffer->events);
                        local_inc(&buffer->wakeup);
                }
        }

        perf_output_put_handle(handle);
        rcu_read_unlock();
}

static u32 perf_event_pid(struct perf_event *event, struct task_struct *p)
{
        /*
         * only top level events have the pid namespace they were created in
         */
        if (event->parent)
                event = event->parent;

        return task_tgid_nr_ns(p, event->ns);
}

static u32 perf_event_tid(struct perf_event *event, struct task_struct *p)
{
        /*
         * only top level events have the pid namespace they were created in
         */
        if (event->parent)
                event = event->parent;

        return task_pid_nr_ns(p, event->ns);
}

static void perf_output_read_one(struct perf_output_handle *handle,
                                 struct perf_event *event)
{
        u64 read_format = event->attr.read_format;
        u64 values[4];
        int n = 0;

        values[n++] = perf_event_count(event);
        if (read_format & PERF_FORMAT_TOTAL_TIME_ENABLED) {
                values[n++] = event->total_time_enabled +
                        atomic64_read(&event->child_total_time_enabled);
        }
        if (read_format & PERF_FORMAT_TOTAL_TIME_RUNNING) {
                values[n++] = event->total_time_running +
                        atomic64_read(&event->child_total_time_running);
        }
        if (read_format & PERF_FORMAT_ID)
                values[n++] = primary_event_id(event);

        perf_output_copy(handle, values, n * sizeof(u64));
}

/*
 * XXX PERF_FORMAT_GROUP vs inherited events seems difficult.
 */
static void perf_output_read_group(struct perf_output_handle *handle,
                            struct perf_event *event)
{
        struct perf_event *leader = event->group_leader, *sub;
        u64 read_format = event->attr.read_format;
        u64 values[5];
        int n = 0;

        values[n++] = 1 + leader->nr_siblings;

        if (read_format & PERF_FORMAT_TOTAL_TIME_ENABLED)
                values[n++] = leader->total_time_enabled;

        if (read_format & PERF_FORMAT_TOTAL_TIME_RUNNING)
                values[n++] = leader->total_time_running;

        if (leader != event)
                leader->pmu->read(leader);

        values[n++] = perf_event_count(leader);
        if (read_format & PERF_FORMAT_ID)
                values[n++] = primary_event_id(leader);

        perf_output_copy(handle, values, n * sizeof(u64));

        list_for_each_entry(sub, &leader->sibling_list, group_entry) {
                n = 0;

                if (sub != event)
                        sub->pmu->read(sub);

                values[n++] = perf_event_count(sub);
                if (read_format & PERF_FORMAT_ID)
                        values[n++] = primary_event_id(sub);

                perf_output_copy(handle, values, n * sizeof(u64));
        }
}

static void perf_output_read(struct perf_output_handle *handle,
                             struct perf_event *event)
{
        if (event->attr.read_format & PERF_FORMAT_GROUP)
                perf_output_read_group(handle, event);
        else
                perf_output_read_one(handle, event);
}

void perf_output_sample(struct perf_output_handle *handle,
                        struct perf_event_header *header,
                        struct perf_sample_data *data,
                        struct perf_event *event)
{
        u64 sample_type = data->type;

        perf_output_put(handle, *header);

        if (sample_type & PERF_SAMPLE_IP)
                perf_output_put(handle, data->ip);

        if (sample_type & PERF_SAMPLE_TID)
                perf_output_put(handle, data->tid_entry);

        if (sample_type & PERF_SAMPLE_TIME)
                perf_output_put(handle, data->time);

        if (sample_type & PERF_SAMPLE_ADDR)
                perf_output_put(handle, data->addr);

        if (sample_type & PERF_SAMPLE_ID)
                perf_output_put(handle, data->id);

        if (sample_type & PERF_SAMPLE_STREAM_ID)
                perf_output_put(handle, data->stream_id);

        if (sample_type & PERF_SAMPLE_CPU)
                perf_output_put(handle, data->cpu_entry);

        if (sample_type & PERF_SAMPLE_PERIOD)
                perf_output_put(handle, data->period);

        if (sample_type & PERF_SAMPLE_READ)
                perf_output_read(handle, event);

        if (sample_type & PERF_SAMPLE_CALLCHAIN) {
                if (data->callchain) {
                        int size = 1;

                        if (data->callchain)
                                size += data->callchain->nr;

                        size *= sizeof(u64);

                        perf_output_copy(handle, data->callchain, size);
                } else {
                        u64 nr = 0;
                        perf_output_put(handle, nr);
                }
        }

        if (sample_type & PERF_SAMPLE_RAW) {
                if (data->raw) {
                        perf_output_put(handle, data->raw->size);
                        perf_output_copy(handle, data->raw->data,
                                         data->raw->size);
                } else {
                        struct {
                                u32     size;
                                u32     data;
                        } raw = {
                                .size = sizeof(u32),
                                .data = 0,
                        };
                        perf_output_put(handle, raw);
                }
        }
}

void perf_prepare_sample(struct perf_event_header *header,
                         struct perf_sample_data *data,
                         struct perf_event *event,
                         struct pt_regs *regs)
{
        u64 sample_type = event->attr.sample_type;

        data->type = sample_type;

        header->type = PERF_RECORD_SAMPLE;
        header->size = sizeof(*header);

        header->misc = 0;
        header->misc |= perf_misc_flags(regs);

        if (sample_type & PERF_SAMPLE_IP) {
                data->ip = perf_instruction_pointer(regs);

                header->size += sizeof(data->ip);
        }

        if (sample_type & PERF_SAMPLE_TID) {
                /* namespace issues */
                data->tid_entry.pid = perf_event_pid(event, current);
                data->tid_entry.tid = perf_event_tid(event, current);

                header->size += sizeof(data->tid_entry);
        }

        if (sample_type & PERF_SAMPLE_TIME) {
                data->time = perf_clock();

                header->size += sizeof(data->time);
        }

        if (sample_type & PERF_SAMPLE_ADDR)
                header->size += sizeof(data->addr);

        if (sample_type & PERF_SAMPLE_ID) {
                data->id = primary_event_id(event);

                header->size += sizeof(data->id);
        }

        if (sample_type & PERF_SAMPLE_STREAM_ID) {
                data->stream_id = event->id;

                header->size += sizeof(data->stream_id);
        }

        if (sample_type & PERF_SAMPLE_CPU) {
                data->cpu_entry.cpu             = raw_smp_processor_id();
                data->cpu_entry.reserved        = 0;

                header->size += sizeof(data->cpu_entry);
        }

        if (sample_type & PERF_SAMPLE_PERIOD)
                header->size += sizeof(data->period);

        if (sample_type & PERF_SAMPLE_READ)
                header->size += perf_event_read_size(event);

        if (sample_type & PERF_SAMPLE_CALLCHAIN) {
                int size = 1;

                data->callchain = perf_callchain(regs);

                if (data->callchain)
                        size += data->callchain->nr;

                header->size += size * sizeof(u64);
        }

        if (sample_type & PERF_SAMPLE_RAW) {
                int size = sizeof(u32);

                if (data->raw)
                        size += data->raw->size;
                else
                        size += sizeof(u32);

                WARN_ON_ONCE(size & (sizeof(u64)-1));
                header->size += size;
        }
}

static void perf_event_output(struct perf_event *event, int nmi,
                                struct perf_sample_data *data,
                                struct pt_regs *regs)
{
        struct perf_output_handle handle;
        struct perf_event_header header;

        perf_prepare_sample(&header, data, event, regs);

        if (perf_output_begin(&handle, event, header.size, nmi, 1))
                return;

        perf_output_sample(&handle, &header, data, event);

        perf_output_end(&handle);
}

/*
 * read event_id
 */

struct perf_read_event {
        struct perf_event_header        header;

        u32                             pid;
        u32                             tid;
};

static void
perf_event_read_event(struct perf_event *event,
                        struct task_struct *task)
{
        struct perf_output_handle handle;
        struct perf_read_event read_event = {
                .header = {
                        .type = PERF_RECORD_READ,
                        .misc = 0,
                        .size = sizeof(read_event) + perf_event_read_size(event),
                },
                .pid = perf_event_pid(event, task),
                .tid = perf_event_tid(event, task),
        };
        int ret;

        ret = perf_output_begin(&handle, event, read_event.header.size, 0, 0);
        if (ret)
                return;

        perf_output_put(&handle, read_event);
        perf_output_read(&handle, event);

        perf_output_end(&handle);
}

/*
 * task tracking -- fork/exit
 *
 * enabled by: attr.comm | attr.mmap | attr.mmap_data | attr.task
 */

struct perf_task_event {
        struct task_struct              *task;
        struct perf_event_context       *task_ctx;

        struct {
                struct perf_event_header        header;

                u32                             pid;
                u32                             ppid;
                u32                             tid;
                u32                             ptid;
                u64                             time;
        } event_id;
};

static void perf_event_task_output(struct perf_event *event,
                                     struct perf_task_event *task_event)
{
        struct perf_output_handle handle;
        struct task_struct *task = task_event->task;
        int size, ret;

        size  = task_event->event_id.header.size;
        ret = perf_output_begin(&handle, event, size, 0, 0);

        if (ret)
                return;

        task_event->event_id.pid = perf_event_pid(event, task);
        task_event->event_id.ppid = perf_event_pid(event, current);

        task_event->event_id.tid = perf_event_tid(event, task);
        task_event->event_id.ptid = perf_event_tid(event, current);

        perf_output_put(&handle, task_event->event_id);

        perf_output_end(&handle);
}

static int perf_event_task_match(struct perf_event *event)
{
        if (event->state < PERF_EVENT_STATE_INACTIVE)
                return 0;

        if (event->cpu != -1 && event->cpu != smp_processor_id())
                return 0;

        if (event->attr.comm || event->attr.mmap ||
            event->attr.mmap_data || event->attr.task)
                return 1;

        return 0;
}

static void perf_event_task_ctx(struct perf_event_context *ctx,
                                  struct perf_task_event *task_event)
{
        struct perf_event *event;

        list_for_each_entry_rcu(event, &ctx->event_list, event_entry) {
                if (perf_event_task_match(event))
                        perf_event_task_output(event, task_event);
        }
}

static void perf_event_task_event(struct perf_task_event *task_event)
{
        struct perf_cpu_context *cpuctx;
        struct perf_event_context *ctx = task_event->task_ctx;

        rcu_read_lock();
        cpuctx = &get_cpu_var(perf_cpu_context);
        perf_event_task_ctx(&cpuctx->ctx, task_event);
        if (!ctx)
                ctx = rcu_dereference(current->perf_event_ctxp);
        if (ctx)
                perf_event_task_ctx(ctx, task_event);
        put_cpu_var(perf_cpu_context);
        rcu_read_unlock();
}

static void perf_event_task(struct task_struct *task,
                              struct perf_event_context *task_ctx,
                              int new)
{
        struct perf_task_event task_event;

        if (!atomic_read(&nr_comm_events) &&
            !atomic_read(&nr_mmap_events) &&
            !atomic_read(&nr_task_events))
                return;

        task_event = (struct perf_task_event){
                .task     = task,
                .task_ctx = task_ctx,
                .event_id    = {
                        .header = {
                                .type = new ? PERF_RECORD_FORK : PERF_RECORD_EXIT,
                                .misc = 0,
                                .size = sizeof(task_event.event_id),
                        },
                        /* .pid  */
                        /* .ppid */
                        /* .tid  */
                        /* .ptid */
                        .time = perf_clock(),
                },
        };

        perf_event_task_event(&task_event);
}

void perf_event_fork(struct task_struct *task)
{
        perf_event_task(task, NULL, 1);
}

/*
 * comm tracking
 */

struct perf_comm_event {
        struct task_struct      *task;
        char                    *comm;
        int                     comm_size;

        struct {
                struct perf_event_header        header;

                u32                             pid;
                u32                             tid;
        } event_id;
};

static void perf_event_comm_output(struct perf_event *event,
                                     struct perf_comm_event *comm_event)
{
        struct perf_output_handle handle;
        int size = comm_event->event_id.header.size;
        int ret = perf_output_begin(&handle, event, size, 0, 0);

        if (ret)
                return;

        comm_event->event_id.pid = perf_event_pid(event, comm_event->task);
        comm_event->event_id.tid = perf_event_tid(event, comm_event->task);

        perf_output_put(&handle, comm_event->event_id);
        perf_output_copy(&handle, comm_event->comm,
                                   comm_event->comm_size);
        perf_output_end(&handle);
}

static int perf_event_comm_match(struct perf_event *event)
{
        if (event->state < PERF_EVENT_STATE_INACTIVE)
                return 0;

        if (event->cpu != -1 && event->cpu != smp_processor_id())
                return 0;

        if (event->attr.comm)
                return 1;

        return 0;
}

static void perf_event_comm_ctx(struct perf_event_context *ctx,
                                  struct perf_comm_event *comm_event)
{
        struct perf_event *event;

        list_for_each_entry_rcu(event, &ctx->event_list, event_entry) {
                if (perf_event_comm_match(event))
                        perf_event_comm_output(event, comm_event);
        }
}

static void perf_event_comm_event(struct perf_comm_event *comm_event)
{
        struct perf_cpu_context *cpuctx;
        struct perf_event_context *ctx;
        unsigned int size;
        char comm[TASK_COMM_LEN];

        memset(comm, 0, sizeof(comm));
        strlcpy(comm, comm_event->task->comm, sizeof(comm));
        size = ALIGN(strlen(comm)+1, sizeof(u64));

        comm_event->comm = comm;
        comm_event->comm_size = size;

        comm_event->event_id.header.size = sizeof(comm_event->event_id) + size;

        rcu_read_lock();
        cpuctx = &get_cpu_var(perf_cpu_context);
        perf_event_comm_ctx(&cpuctx->ctx, comm_event);
        ctx = rcu_dereference(current->perf_event_ctxp);
        if (ctx)
                perf_event_comm_ctx(ctx, comm_event);
        put_cpu_var(perf_cpu_context);
        rcu_read_unlock();
}

void perf_event_comm(struct task_struct *task)
{
        struct perf_comm_event comm_event;

        if (task->perf_event_ctxp)
                perf_event_enable_on_exec(task);

        if (!atomic_read(&nr_comm_events))
                return;

        comm_event = (struct perf_comm_event){
                .task   = task,
                /* .comm      */
                /* .comm_size */
                .event_id  = {
                        .header = {
                                .type = PERF_RECORD_COMM,
                                .misc = 0,
                                /* .size */
                        },
                        /* .pid */
                        /* .tid */
                },
        };

        perf_event_comm_event(&comm_event);
}

/*
 * mmap tracking
 */

struct perf_mmap_event {
        struct vm_area_struct   *vma;

        const char              *file_name;
        int                     file_size;

        struct {
                struct perf_event_header        header;

                u32                             pid;
                u32                             tid;
                u64                             start;
                u64                             len;
                u64                             pgoff;
        } event_id;
};

static void perf_event_mmap_output(struct perf_event *event,
                                     struct perf_mmap_event *mmap_event)
{
        struct perf_output_handle handle;
        int size = mmap_event->event_id.header.size;
        int ret = perf_output_begin(&handle, event, size, 0, 0);

        if (ret)
                return;

        mmap_event->event_id.pid = perf_event_pid(event, current);
        mmap_event->event_id.tid = perf_event_tid(event, current);

        perf_output_put(&handle, mmap_event->event_id);
        perf_output_copy(&handle, mmap_event->file_name,
                                   mmap_event->file_size);
        perf_output_end(&handle);
}

static int perf_event_mmap_match(struct perf_event *event,
                                   struct perf_mmap_event *mmap_event,
                                   int executable)
{
        if (event->state < PERF_EVENT_STATE_INACTIVE)
                return 0;

        if (event->cpu != -1 && event->cpu != smp_processor_id())
                return 0;

        if ((!executable && event->attr.mmap_data) ||
            (executable && event->attr.mmap))
                return 1;

        return 0;
}

static void perf_event_mmap_ctx(struct perf_event_context *ctx,
                                  struct perf_mmap_event *mmap_event,
                                  int executable)
{
        struct perf_event *event;

        list_for_each_entry_rcu(event, &ctx->event_list, event_entry) {
                if (perf_event_mmap_match(event, mmap_event, executable))
                        perf_event_mmap_output(event, mmap_event);
        }
}

static void perf_event_mmap_event(struct perf_mmap_event *mmap_event)
{
        struct perf_cpu_context *cpuctx;
        struct perf_event_context *ctx;
        struct vm_area_struct *vma = mmap_event->vma;
        struct file *file = vma->vm_file;
        unsigned int size;
        char tmp[16];
        char *buf = NULL;
        const char *name;

        memset(tmp, 0, sizeof(tmp));

        if (file) {
                /*
                 * d_path works from the end of the buffer backwards, so we
                 * need to add enough zero bytes after the string to handle
                 * the 64bit alignment we do later.
                 */
                buf = kzalloc(PATH_MAX + sizeof(u64), GFP_KERNEL);
                if (!buf) {
                        name = strncpy(tmp, "//enomem", sizeof(tmp));
                        goto got_name;
                }
                name = d_path(&file->f_path, buf, PATH_MAX);
                if (IS_ERR(name)) {
                        name = strncpy(tmp, "//toolong", sizeof(tmp));
                        goto got_name;
                }
        } else {
                if (arch_vma_name(mmap_event->vma)) {
                        name = strncpy(tmp, arch_vma_name(mmap_event->vma),
                                       sizeof(tmp));
                        goto got_name;
                }

                if (!vma->vm_mm) {
                        name = strncpy(tmp, "[vdso]", sizeof(tmp));
                        goto got_name;
                } else if (vma->vm_start <= vma->vm_mm->start_brk &&
                                vma->vm_end >= vma->vm_mm->brk) {
                        name = strncpy(tmp, "[heap]", sizeof(tmp));
                        goto got_name;
                } else if (vma->vm_start <= vma->vm_mm->start_stack &&
                                vma->vm_end >= vma->vm_mm->start_stack) {
                        name = strncpy(tmp, "[stack]", sizeof(tmp));
                        goto got_name;
                }

                name = strncpy(tmp, "//anon", sizeof(tmp));
                goto got_name;
        }

got_name:
        size = ALIGN(strlen(name)+1, sizeof(u64));

        mmap_event->file_name = name;
        mmap_event->file_size = size;

        mmap_event->event_id.header.size = sizeof(mmap_event->event_id) + size;

        rcu_read_lock();
        cpuctx = &get_cpu_var(perf_cpu_context);
        perf_event_mmap_ctx(&cpuctx->ctx, mmap_event, vma->vm_flags & VM_EXEC);
        ctx = rcu_dereference(current->perf_event_ctxp);
        if (ctx)
                perf_event_mmap_ctx(ctx, mmap_event, vma->vm_flags & VM_EXEC);
        put_cpu_var(perf_cpu_context);
        rcu_read_unlock();

        kfree(buf);
}

void perf_event_mmap(struct vm_area_struct *vma)
{
        struct perf_mmap_event mmap_event;

        if (!atomic_read(&nr_mmap_events))
                return;

        mmap_event = (struct perf_mmap_event){
                .vma    = vma,
                /* .file_name */
                /* .file_size */
                .event_id  = {
                        .header = {
                                .type = PERF_RECORD_MMAP,
                                .misc = PERF_RECORD_MISC_USER,
                                /* .size */
                        },
                        /* .pid */
                        /* .tid */
                        .start  = vma->vm_start,
                        .len    = vma->vm_end - vma->vm_start,
                        .pgoff  = (u64)vma->vm_pgoff << PAGE_SHIFT,
                },
        };

        perf_event_mmap_event(&mmap_event);
}

/*
 * IRQ throttle logging
 */

static void perf_log_throttle(struct perf_event *event, int enable)
{
        struct perf_output_handle handle;
        int ret;

        struct {
                struct perf_event_header        header;
                u64                             time;
                u64                             id;
                u64                             stream_id;
        } throttle_event = {
                .header = {
                        .type = PERF_RECORD_THROTTLE,
                        .misc = 0,
                        .size = sizeof(throttle_event),
                },
                .time           = perf_clock(),
                .id             = primary_event_id(event),
                .stream_id      = event->id,
        };

        if (enable)
                throttle_event.header.type = PERF_RECORD_UNTHROTTLE;

        ret = perf_output_begin(&handle, event, sizeof(throttle_event), 1, 0);
        if (ret)
                return;

        perf_output_put(&handle, throttle_event);
        perf_output_end(&handle);
}

/*
 * Generic event overflow handling, sampling.
 */

static int __perf_event_overflow(struct perf_event *event, int nmi,
                                   int throttle, struct perf_sample_data *data,
                                   struct pt_regs *regs)
{
        int events = atomic_read(&event->event_limit);
        struct hw_perf_event *hwc = &event->hw;
        int ret = 0;

        throttle = (throttle && event->pmu->unthrottle != NULL);

        if (!throttle) {
                hwc->interrupts++;
        } else {
                if (hwc->interrupts != MAX_INTERRUPTS) {
                        hwc->interrupts++;
                        if (HZ * hwc->interrupts >
                                        (u64)sysctl_perf_event_sample_rate) {
                                hwc->interrupts = MAX_INTERRUPTS;
                                perf_log_throttle(event, 0);
                                ret = 1;
                        }
                } else {
                        /*
                         * Keep re-disabling events even though on the previous
                         * pass we disabled it - just in case we raced with a
                         * sched-in and the event got enabled again:
                         */
                        ret = 1;
                }
        }

        if (event->attr.freq) {
                u64 now = perf_clock();
                s64 delta = now - hwc->freq_time_stamp;

                hwc->freq_time_stamp = now;

                if (delta > 0 && delta < 2*TICK_NSEC)
                        perf_adjust_period(event, delta, hwc->last_period);
        }

        /*
         * XXX event_limit might not quite work as expected on inherited
         * events
         */

        event->pending_kill = POLL_IN;
        if (events && atomic_dec_and_test(&event->event_limit)) {
                ret = 1;
                event->pending_kill = POLL_HUP;
                if (nmi) {
                        event->pending_disable = 1;
                        perf_pending_queue(&event->pending,
                                           perf_pending_event);
                } else
                        perf_event_disable(event);
        }

        if (event->overflow_handler)
                event->overflow_handler(event, nmi, data, regs);
        else
                perf_event_output(event, nmi, data, regs);

        return ret;
}

int perf_event_overflow(struct perf_event *event, int nmi,
                          struct perf_sample_data *data,
                          struct pt_regs *regs)
{
        return __perf_event_overflow(event, nmi, 1, data, regs);
}

/*
 * Generic software event infrastructure
 */

/*
 * We directly increment event->count and keep a second value in
 * event->hw.period_left to count intervals. This period event
 * is kept in the range [-sample_period, 0] so that we can use the
 * sign as trigger.
 */

static u64 perf_swevent_set_period(struct perf_event *event)
{
        struct hw_perf_event *hwc = &event->hw;
        u64 period = hwc->last_period;
        u64 nr, offset;
        s64 old, val;

        hwc->last_period = hwc->sample_period;

again:
        old = val = local64_read(&hwc->period_left);
        if (val < 0)
                return 0;

        nr = div64_u64(period + val, period);
        offset = nr * period;
        val -= offset;
        if (local64_cmpxchg(&hwc->period_left, old, val) != old)
                goto again;

        return nr;
}

static void perf_swevent_overflow(struct perf_event *event, u64 overflow,
                                    int nmi, struct perf_sample_data *data,
                                    struct pt_regs *regs)
{
        struct hw_perf_event *hwc = &event->hw;
        int throttle = 0;

        data->period = event->hw.last_period;
        if (!overflow)
                overflow = perf_swevent_set_period(event);

        if (hwc->interrupts == MAX_INTERRUPTS)
                return;

        for (; overflow; overflow--) {
                if (__perf_event_overflow(event, nmi, throttle,
                                            data, regs)) {
                        /*
                         * We inhibit the overflow from happening when
                         * hwc->interrupts == MAX_INTERRUPTS.
                         */
                        break;
                }
                throttle = 1;
        }
}

static void perf_swevent_add(struct perf_event *event, u64 nr,
                               int nmi, struct perf_sample_data *data,
                               struct pt_regs *regs)
{
        struct hw_perf_event *hwc = &event->hw;

        local64_add(nr, &event->count);

        if (!regs)
                return;

        if (!hwc->sample_period)
                return;

        if (nr == 1 && hwc->sample_period == 1 && !event->attr.freq)
                return perf_swevent_overflow(event, 1, nmi, data, regs);

        if (local64_add_negative(nr, &hwc->period_left))
                return;

        perf_swevent_overflow(event, 0, nmi, data, regs);
}

static int perf_exclude_event(struct perf_event *event,
                              struct pt_regs *regs)
{
        if (regs) {
                if (event->attr.exclude_user && user_mode(regs))
                        return 1;

                if (event->attr.exclude_kernel && !user_mode(regs))
                        return 1;
        }

        return 0;
}

static int perf_swevent_match(struct perf_event *event,
                                enum perf_type_id type,
                                u32 event_id,
                                struct perf_sample_data *data,
                                struct pt_regs *regs)
{
        if (event->attr.type != type)
                return 0;

        if (event->attr.config != event_id)
                return 0;

        if (perf_exclude_event(event, regs))
                return 0;

        return 1;
}

static inline u64 swevent_hash(u64 type, u32 event_id)
{
        u64 val = event_id | (type << 32);

        return hash_64(val, SWEVENT_HLIST_BITS);
}

static inline struct hlist_head *
__find_swevent_head(struct swevent_hlist *hlist, u64 type, u32 event_id)
{
        u64 hash = swevent_hash(type, event_id);

        return &hlist->heads[hash];
}

/* For the read side: events when they trigger */
static inline struct hlist_head *
find_swevent_head_rcu(struct perf_cpu_context *ctx, u64 type, u32 event_id)
{
        struct swevent_hlist *hlist;

        hlist = rcu_dereference(ctx->swevent_hlist);
        if (!hlist)
                return NULL;

        return __find_swevent_head(hlist, type, event_id);
}

/* For the event head insertion and removal in the hlist */
static inline struct hlist_head *
find_swevent_head(struct perf_cpu_context *ctx, struct perf_event *event)
{
        struct swevent_hlist *hlist;
        u32 event_id = event->attr.config;
        u64 type = event->attr.type;

        /*
         * Event scheduling is always serialized against hlist allocation
         * and release. Which makes the protected version suitable here.
         * The context lock guarantees that.
         */
        hlist = rcu_dereference_protected(ctx->swevent_hlist,
                                          lockdep_is_held(&event->ctx->lock));
        if (!hlist)
                return NULL;

        return __find_swevent_head(hlist, type, event_id);
}

static void do_perf_sw_event(enum perf_type_id type, u32 event_id,
                                    u64 nr, int nmi,
                                    struct perf_sample_data *data,
                                    struct pt_regs *regs)
{
        struct perf_cpu_context *cpuctx;
        struct perf_event *event;
        struct hlist_node *node;
        struct hlist_head *head;

        cpuctx = &__get_cpu_var(perf_cpu_context);

        rcu_read_lock();

        head = find_swevent_head_rcu(cpuctx, type, event_id);

        if (!head)
                goto end;

        hlist_for_each_entry_rcu(event, node, head, hlist_entry) {
                if (perf_swevent_match(event, type, event_id, data, regs))
                        perf_swevent_add(event, nr, nmi, data, regs);
        }
end:
        rcu_read_unlock();
}

int perf_swevent_get_recursion_context(void)
{
        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
        int rctx;

        if (in_nmi())
                rctx = 3;
        else if (in_irq())
                rctx = 2;
        else if (in_softirq())
                rctx = 1;
        else
                rctx = 0;

        if (cpuctx->recursion[rctx])
                return -1;

        cpuctx->recursion[rctx]++;
        barrier();

        return rctx;
}
EXPORT_SYMBOL_GPL(perf_swevent_get_recursion_context);

void inline perf_swevent_put_recursion_context(int rctx)
{
        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
        barrier();
        cpuctx->recursion[rctx]--;
}

void __perf_sw_event(u32 event_id, u64 nr, int nmi,
                            struct pt_regs *regs, u64 addr)
{
        struct perf_sample_data data;
        int rctx;

        preempt_disable_notrace();
        rctx = perf_swevent_get_recursion_context();
        if (rctx < 0)
                return;

        perf_sample_data_init(&data, addr);

        do_perf_sw_event(PERF_TYPE_SOFTWARE, event_id, nr, nmi, &data, regs);

        perf_swevent_put_recursion_context(rctx);
        preempt_enable_notrace();
}

static void perf_swevent_read(struct perf_event *event)
{
}

static int perf_swevent_enable(struct perf_event *event)
{
        struct hw_perf_event *hwc = &event->hw;
        struct perf_cpu_context *cpuctx;
        struct hlist_head *head;

        cpuctx = &__get_cpu_var(perf_cpu_context);

        if (hwc->sample_period) {
                hwc->last_period = hwc->sample_period;
                perf_swevent_set_period(event);
        }

        head = find_swevent_head(cpuctx, event);
        if (WARN_ON_ONCE(!head))
                return -EINVAL;

        hlist_add_head_rcu(&event->hlist_entry, head);

        return 0;
}

static void perf_swevent_disable(struct perf_event *event)
{
        hlist_del_rcu(&event->hlist_entry);
}

static void perf_swevent_void(struct perf_event *event)
{
}

static int perf_swevent_int(struct perf_event *event)
{
        return 0;
}

static const struct pmu perf_ops_generic = {
        .enable         = perf_swevent_enable,
        .disable        = perf_swevent_disable,
        .start          = perf_swevent_int,
        .stop           = perf_swevent_void,
        .read           = perf_swevent_read,
        .unthrottle     = perf_swevent_void, /* hwc->interrupts already reset */
};

/*
 * hrtimer based swevent callback
 */

static enum hrtimer_restart perf_swevent_hrtimer(struct hrtimer *hrtimer)
{
        enum hrtimer_restart ret = HRTIMER_RESTART;
        struct perf_sample_data data;
        struct pt_regs *regs;
        struct perf_event *event;
        u64 period;

        event = container_of(hrtimer, struct perf_event, hw.hrtimer);
        event->pmu->read(event);

        perf_sample_data_init(&data, 0);
        data.period = event->hw.last_period;
        regs = get_irq_regs();

        if (regs && !perf_exclude_event(event, regs)) {
                if (!(event->attr.exclude_idle && current->pid == 0))
                        if (perf_event_overflow(event, 0, &data, regs))
                                ret = HRTIMER_NORESTART;
        }

        period = max_t(u64, 10000, event->hw.sample_period);
        hrtimer_forward_now(hrtimer, ns_to_ktime(period));

        return ret;
}

static void perf_swevent_start_hrtimer(struct perf_event *event)
{
        struct hw_perf_event *hwc = &event->hw;

        hrtimer_init(&hwc->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
        hwc->hrtimer.function = perf_swevent_hrtimer;
        if (hwc->sample_period) {
                u64 period;

                if (hwc->remaining) {
                        if (hwc->remaining < 0)
                                period = 10000;
                        else
                                period = hwc->remaining;
                        hwc->remaining = 0;
                } else {
                        period = max_t(u64, 10000, hwc->sample_period);
                }
                __hrtimer_start_range_ns(&hwc->hrtimer,
                                ns_to_ktime(period), 0,
                                HRTIMER_MODE_REL, 0);
        }
}

static void perf_swevent_cancel_hrtimer(struct perf_event *event)
{
        struct hw_perf_event *hwc = &event->hw;

        if (hwc->sample_period) {
                ktime_t remaining = hrtimer_get_remaining(&hwc->hrtimer);
                hwc->remaining = ktime_to_ns(remaining);

                hrtimer_cancel(&hwc->hrtimer);
        }
}

/*
 * Software event: cpu wall time clock
 */

static void cpu_clock_perf_event_update(struct perf_event *event)
{
        int cpu = raw_smp_processor_id();
        s64 prev;
        u64 now;

        now = cpu_clock(cpu);
        prev = local64_xchg(&event->hw.prev_count, now);
        local64_add(now - prev, &event->count);
}

static int cpu_clock_perf_event_enable(struct perf_event *event)
{
        struct hw_perf_event *hwc = &event->hw;
        int cpu = raw_smp_processor_id();

        local64_set(&hwc->prev_count, cpu_clock(cpu));
        perf_swevent_start_hrtimer(event);

        return 0;
}

static void cpu_clock_perf_event_disable(struct perf_event *event)
{
        perf_swevent_cancel_hrtimer(event);
        cpu_clock_perf_event_update(event);
}

static void cpu_clock_perf_event_read(struct perf_event *event)
{
        cpu_clock_perf_event_update(event);
}

static const struct pmu perf_ops_cpu_clock = {
        .enable         = cpu_clock_perf_event_enable,
        .disable        = cpu_clock_perf_event_disable,
        .read           = cpu_clock_perf_event_read,
};

/*
 * Software event: task time clock
 */

static void task_clock_perf_event_update(struct perf_event *event, u64 now)
{
        u64 prev;
        s64 delta;

        prev = local64_xchg(&event->hw.prev_count, now);
        delta = now - prev;
        local64_add(delta, &event->count);
}

static int task_clock_perf_event_enable(struct perf_event *event)
{
        struct hw_perf_event *hwc = &event->hw;
        u64 now;

        now = event->ctx->time;

        local64_set(&hwc->prev_count, now);

        perf_swevent_start_hrtimer(event);

        return 0;
}

static void task_clock_perf_event_disable(struct perf_event *event)
{
        perf_swevent_cancel_hrtimer(event);
        task_clock_perf_event_update(event, event->ctx->time);

}

static void task_clock_perf_event_read(struct perf_event *event)
{
        u64 time;

        if (!in_nmi()) {
                update_context_time(event->ctx);
                time = event->ctx->time;
        } else {
                u64 now = perf_clock();
                u64 delta = now - event->ctx->timestamp;
                time = event->ctx->time + delta;
        }

        task_clock_perf_event_update(event, time);
}

static const struct pmu perf_ops_task_clock = {
        .enable         = task_clock_perf_event_enable,
        .disable        = task_clock_perf_event_disable,
        .read           = task_clock_perf_event_read,
};

/* Deref the hlist from the update side */
static inline struct swevent_hlist *
swevent_hlist_deref(struct perf_cpu_context *cpuctx)
{
        return rcu_dereference_protected(cpuctx->swevent_hlist,
                                         lockdep_is_held(&cpuctx->hlist_mutex));
}

static void swevent_hlist_release_rcu(struct rcu_head *rcu_head)
{
        struct swevent_hlist *hlist;

        hlist = container_of(rcu_head, struct swevent_hlist, rcu_head);
        kfree(hlist);
}

static void swevent_hlist_release(struct perf_cpu_context *cpuctx)
{
        struct swevent_hlist *hlist = swevent_hlist_deref(cpuctx);

        if (!hlist)
                return;

        rcu_assign_pointer(cpuctx->swevent_hlist, NULL);
        call_rcu(&hlist->rcu_head, swevent_hlist_release_rcu);
}

static void swevent_hlist_put_cpu(struct perf_event *event, int cpu)
{
        struct perf_cpu_context *cpuctx = &per_cpu(perf_cpu_context, cpu);

        mutex_lock(&cpuctx->hlist_mutex);

        if (!--cpuctx->hlist_refcount)
                swevent_hlist_release(cpuctx);

        mutex_unlock(&cpuctx->hlist_mutex);
}

static void swevent_hlist_put(struct perf_event *event)
{
        int cpu;

        if (event->cpu != -1) {
                swevent_hlist_put_cpu(event, event->cpu);
                return;
        }

        for_each_possible_cpu(cpu)
                swevent_hlist_put_cpu(event, cpu);
}

static int swevent_hlist_get_cpu(struct perf_event *event, int cpu)
{
        struct perf_cpu_context *cpuctx = &per_cpu(perf_cpu_context, cpu);
        int err = 0;

        mutex_lock(&cpuctx->hlist_mutex);

        if (!swevent_hlist_deref(cpuctx) && cpu_online(cpu)) {
                struct swevent_hlist *hlist;

                hlist = kzalloc(sizeof(*hlist), GFP_KERNEL);
                if (!hlist) {
                        err = -ENOMEM;
                        goto exit;
                }
                rcu_assign_pointer(cpuctx->swevent_hlist, hlist);
        }
        cpuctx->hlist_refcount++;
 exit:
        mutex_unlock(&cpuctx->hlist_mutex);

        return err;
}

static int swevent_hlist_get(struct perf_event *event)
{
        int err;
        int cpu, failed_cpu;

        if (event->cpu != -1)
                return swevent_hlist_get_cpu(event, event->cpu);

        get_online_cpus();
        for_each_possible_cpu(cpu) {
                err = swevent_hlist_get_cpu(event, cpu);
                if (err) {
                        failed_cpu = cpu;
                        goto fail;
                }
        }
        put_online_cpus();

        return 0;
 fail:
        for_each_possible_cpu(cpu) {
                if (cpu == failed_cpu)
                        break;
                swevent_hlist_put_cpu(event, cpu);
        }

        put_online_cpus();
        return err;
}

#ifdef CONFIG_EVENT_TRACING

static const struct pmu perf_ops_tracepoint = {
        .enable         = perf_trace_enable,
        .disable        = perf_trace_disable,
        .start          = perf_swevent_int,
        .stop           = perf_swevent_void,
        .read           = perf_swevent_read,
        .unthrottle     = perf_swevent_void,
};

static int perf_tp_filter_match(struct perf_event *event,
                                struct perf_sample_data *data)
{
        void *record = data->raw->data;

        if (likely(!event->filter) || filter_match_preds(event->filter, record))
                return 1;
        return 0;
}

static int perf_tp_event_match(struct perf_event *event,
                                struct perf_sample_data *data,
                                struct pt_regs *regs)
{
        /*
         * All tracepoints are from kernel-space.
         */
        if (event->attr.exclude_kernel)
                return 0;

        if (!perf_tp_filter_match(event, data))
                return 0;

        return 1;
}

void perf_tp_event(u64 addr, u64 count, void *record, int entry_size,
                   struct pt_regs *regs, struct hlist_head *head, int rctx)
{
        struct perf_sample_data data;
        struct perf_event *event;
        struct hlist_node *node;

        struct perf_raw_record raw = {
                .size = entry_size,
                .data = record,
        };

        perf_sample_data_init(&data, addr);
        data.raw = &raw;

        hlist_for_each_entry_rcu(event, node, head, hlist_entry) {
                if (perf_tp_event_match(event, &data, regs))
                        perf_swevent_add(event, count, 1, &data, regs);
        }

        perf_swevent_put_recursion_context(rctx);
}
EXPORT_SYMBOL_GPL(perf_tp_event);

static void tp_perf_event_destroy(struct perf_event *event)
{
        perf_trace_destroy(event);
}

static const struct pmu *tp_perf_event_init(struct perf_event *event)
{
        int err;

        /*
         * Raw tracepoint data is a severe data leak, only allow root to
         * have these.
         */
        if ((event->attr.sample_type & PERF_SAMPLE_RAW) &&
                        perf_paranoid_tracepoint_raw() &&
                        !capable(CAP_SYS_ADMIN))
                return ERR_PTR(-EPERM);

        err = perf_trace_init(event);
        if (err)
                return NULL;

        event->destroy = tp_perf_event_destroy;

        return &perf_ops_tracepoint;
}

static int perf_event_set_filter(struct perf_event *event, void __user *arg)
{
        char *filter_str;
        int ret;

        if (event->attr.type != PERF_TYPE_TRACEPOINT)
                return -EINVAL;

        filter_str = strndup_user(arg, PAGE_SIZE);
        if (IS_ERR(filter_str))
                return PTR_ERR(filter_str);

        ret = ftrace_profile_set_filter(event, event->attr.config, filter_str);

        kfree(filter_str);
        return ret;
}

static void perf_event_free_filter(struct perf_event *event)
{
        ftrace_profile_free_filter(event);
}

#else

static const struct pmu *tp_perf_event_init(struct perf_event *event)
{
        return NULL;
}

static int perf_event_set_filter(struct perf_event *event, void __user *arg)
{
        return -ENOENT;
}

static void perf_event_free_filter(struct perf_event *event)
{
}

#endif /* CONFIG_EVENT_TRACING */

#ifdef CONFIG_HAVE_HW_BREAKPOINT
static void bp_perf_event_destroy(struct perf_event *event)
{
        release_bp_slot(event);
}

static const struct pmu *bp_perf_event_init(struct perf_event *bp)
{
        int err;

        err = register_perf_hw_breakpoint(bp);
        if (err)
                return ERR_PTR(err);

        bp->destroy = bp_perf_event_destroy;

        return &perf_ops_bp;
}

void perf_bp_event(struct perf_event *bp, void *data)
{
        struct perf_sample_data sample;
        struct pt_regs *regs = data;

        perf_sample_data_init(&sample, bp->attr.bp_addr);

        if (!perf_exclude_event(bp, regs))
                perf_swevent_add(bp, 1, 1, &sample, regs);
}
#else
static const struct pmu *bp_perf_event_init(struct perf_event *bp)
{
        return NULL;
}

void perf_bp_event(struct perf_event *bp, void *regs)
{
}
#endif

atomic_t perf_swevent_enabled[PERF_COUNT_SW_MAX];

static void sw_perf_event_destroy(struct perf_event *event)
{
        u64 event_id = event->attr.config;

        WARN_ON(event->parent);

        atomic_dec(&perf_swevent_enabled[event_id]);
        swevent_hlist_put(event);
}

static const struct pmu *sw_perf_event_init(struct perf_event *event)
{
        const struct pmu *pmu = NULL;
        u64 event_id = event->attr.config;

        /*
         * Software events (currently) can't in general distinguish
         * between user, kernel and hypervisor events.
         * However, context switches and cpu migrations are considered
         * to be kernel events, and page faults are never hypervisor
         * events.
         */
        switch (event_id) {
        case PERF_COUNT_SW_CPU_CLOCK:
                pmu = &perf_ops_cpu_clock;

                break;
        case PERF_COUNT_SW_TASK_CLOCK:
                /*
                 * If the user instantiates this as a per-cpu event,
                 * use the cpu_clock event instead.
                 */
                if (event->ctx->task)
                        pmu = &perf_ops_task_clock;
                else
                        pmu = &perf_ops_cpu_clock;

                break;
        case PERF_COUNT_SW_PAGE_FAULTS:
        case PERF_COUNT_SW_PAGE_FAULTS_MIN:
        case PERF_COUNT_SW_PAGE_FAULTS_MAJ:
        case PERF_COUNT_SW_CONTEXT_SWITCHES:
        case PERF_COUNT_SW_CPU_MIGRATIONS:
        case PERF_COUNT_SW_ALIGNMENT_FAULTS:
        case PERF_COUNT_SW_EMULATION_FAULTS:
                if (!event->parent) {
                        int err;

                        err = swevent_hlist_get(event);
                        if (err)
                                return ERR_PTR(err);

                        atomic_inc(&perf_swevent_enabled[event_id]);
                        event->destroy = sw_perf_event_destroy;
                }
                pmu = &perf_ops_generic;
                break;
        }

        return pmu;
}

/*
 * Allocate and initialize a event structure
 */
static struct perf_event *
perf_event_alloc(struct perf_event_attr *attr,
                   int cpu,
                   struct perf_event_context *ctx,
                   struct perf_event *group_leader,
                   struct perf_event *parent_event,
                   perf_overflow_handler_t overflow_handler,
                   gfp_t gfpflags)
{
        const struct pmu *pmu;
        struct perf_event *event;
        struct hw_perf_event *hwc;
        long err;

        event = kzalloc(sizeof(*event), gfpflags);
        if (!event)
                return ERR_PTR(-ENOMEM);

        /*
         * Single events are their own group leaders, with an
         * empty sibling list:
         */
        if (!group_leader)
                group_leader = event;

        mutex_init(&event->child_mutex);
        INIT_LIST_HEAD(&event->child_list);

        INIT_LIST_HEAD(&event->group_entry);
        INIT_LIST_HEAD(&event->event_entry);
        INIT_LIST_HEAD(&event->sibling_list);
        init_waitqueue_head(&event->waitq);

        mutex_init(&event->mmap_mutex);

        event->cpu              = cpu;
        event->attr             = *attr;
        event->group_leader     = group_leader;
        event->pmu              = NULL;
        event->ctx              = ctx;
        event->oncpu            = -1;

        event->parent           = parent_event;

        event->ns               = get_pid_ns(current->nsproxy->pid_ns);
        event->id               = atomic64_inc_return(&perf_event_id);

        event->state            = PERF_EVENT_STATE_INACTIVE;

        if (!overflow_handler && parent_event)
                overflow_handler = parent_event->overflow_handler;
        
        event->overflow_handler = overflow_handler;

        if (attr->disabled)
                event->state = PERF_EVENT_STATE_OFF;

        pmu = NULL;

        hwc = &event->hw;
        hwc->sample_period = attr->sample_period;
        if (attr->freq && attr->sample_freq)
                hwc->sample_period = 1;
        hwc->last_period = hwc->sample_period;

        local64_set(&hwc->period_left, hwc->sample_period);

        /*
         * we currently do not support PERF_FORMAT_GROUP on inherited events
         */
        if (attr->inherit && (attr->read_format & PERF_FORMAT_GROUP))
                goto done;

        switch (attr->type) {
        case PERF_TYPE_RAW:
        case PERF_TYPE_HARDWARE:
        case PERF_TYPE_HW_CACHE:
                pmu = hw_perf_event_init(event);
                break;

        case PERF_TYPE_SOFTWARE:
                pmu = sw_perf_event_init(event);
                break;

        case PERF_TYPE_TRACEPOINT:
                pmu = tp_perf_event_init(event);
                break;

        case PERF_TYPE_BREAKPOINT:
                pmu = bp_perf_event_init(event);
                break;


        default:
                break;
        }
done:
        err = 0;
        if (!pmu)
                err = -EINVAL;
        else if (IS_ERR(pmu))
                err = PTR_ERR(pmu);

        if (err) {
                if (event->ns)
                        put_pid_ns(event->ns);
                kfree(event);
                return ERR_PTR(err);
        }

        event->pmu = pmu;

        if (!event->parent) {
                atomic_inc(&nr_events);
                if (event->attr.mmap || event->attr.mmap_data)
                        atomic_inc(&nr_mmap_events);
                if (event->attr.comm)
                        atomic_inc(&nr_comm_events);
                if (event->attr.task)
                        atomic_inc(&nr_task_events);
        }

        return event;
}

static int perf_copy_attr(struct perf_event_attr __user *uattr,
                          struct perf_event_attr *attr)
{
        u32 size;
        int ret;

        if (!access_ok(VERIFY_WRITE, uattr, PERF_ATTR_SIZE_VER0))
                return -EFAULT;

        /*
         * zero the full structure, so that a short copy will be nice.
         */
        memset(attr, 0, sizeof(*attr));

        ret = get_user(size, &uattr->size);
        if (ret)
                return ret;

        if (size > PAGE_SIZE)   /* silly large */
                goto err_size;

        if (!size)              /* abi compat */
                size = PERF_ATTR_SIZE_VER0;

        if (size < PERF_ATTR_SIZE_VER0)
                goto err_size;

        /*
         * If we're handed a bigger struct than we know of,
         * ensure all the unknown bits are 0 - i.e. new
         * user-space does not rely on any kernel feature
         * extensions we dont know about yet.
         */
        if (size > sizeof(*attr)) {
                unsigned char __user *addr;
                unsigned char __user *end;
                unsigned char val;

                addr = (void __user *)uattr + sizeof(*attr);
                end  = (void __user *)uattr + size;

                for (; addr < end; addr++) {
                        ret = get_user(val, addr);
                        if (ret)
                                return ret;
                        if (val)
                                goto err_size;
                }
                size = sizeof(*attr);
        }

        ret = copy_from_user(attr, uattr, size);
        if (ret)
                return -EFAULT;

        /*
         * If the type exists, the corresponding creation will verify
         * the attr->config.
         */
        if (attr->type >= PERF_TYPE_MAX)
                return -EINVAL;

        if (attr->__reserved_1)
                return -EINVAL;

        if (attr->sample_type & ~(PERF_SAMPLE_MAX-1))
                return -EINVAL;

        if (attr->read_format & ~(PERF_FORMAT_MAX-1))
                return -EINVAL;

out:
        return ret;

err_size:
        put_user(sizeof(*attr), &uattr->size);
        ret = -E2BIG;
        goto out;
}

static int
perf_event_set_output(struct perf_event *event, struct perf_event *output_event)
{
        struct perf_buffer *buffer = NULL, *old_buffer = NULL;
        int ret = -EINVAL;

        if (!output_event)
                goto set;

        /* don't allow circular references */
        if (event == output_event)
                goto out;

        /*
         * Don't allow cross-cpu buffers
         */
        if (output_event->cpu != event->cpu)
                goto out;

        /*
         * If its not a per-cpu buffer, it must be the same task.
         */
        if (output_event->cpu == -1 && output_event->ctx != event->ctx)
                goto out;

set:
        mutex_lock(&event->mmap_mutex);
        /* Can't redirect output if we've got an active mmap() */
        if (atomic_read(&event->mmap_count))
                goto unlock;

        if (output_event) {
                /* get the buffer we want to redirect to */
                buffer = perf_buffer_get(output_event);
                if (!buffer)
                        goto unlock;
        }

        old_buffer = event->buffer;
        rcu_assign_pointer(event->buffer, buffer);
        ret = 0;
unlock:
        mutex_unlock(&event->mmap_mutex);

        if (old_buffer)
                perf_buffer_put(old_buffer);
out:
        return ret;
}

/**
 * sys_perf_event_open - open a performance event, associate it to a task/cpu
 *
 * @attr_uptr:  event_id type attributes for monitoring/sampling
 * @pid:                target pid
 * @cpu:                target cpu
 * @group_fd:           group leader event fd
 */
SYSCALL_DEFINE5(perf_event_open,
                struct perf_event_attr __user *, attr_uptr,
                pid_t, pid, int, cpu, int, group_fd, unsigned long, flags)
{
        struct perf_event *event, *group_leader = NULL, *output_event = NULL;
        struct perf_event_attr attr;
        struct perf_event_context *ctx;
        struct file *event_file = NULL;
        struct file *group_file = NULL;
        int event_fd;
        int fput_needed = 0;
        int err;

        /* for future expandability... */
        if (flags & ~(PERF_FLAG_FD_NO_GROUP | PERF_FLAG_FD_OUTPUT))
                return -EINVAL;

        err = perf_copy_attr(attr_uptr, &attr);
        if (err)
                return err;

        if (!attr.exclude_kernel) {
                if (perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
                        return -EACCES;
        }

        if (attr.freq) {
                if (attr.sample_freq > sysctl_perf_event_sample_rate)
                        return -EINVAL;
        }

        event_fd = get_unused_fd_flags(O_RDWR);
        if (event_fd < 0)
                return event_fd;

        /*
         * Get the target context (task or percpu):
         */
        ctx = find_get_context(pid, cpu);
        if (IS_ERR(ctx)) {
                err = PTR_ERR(ctx);
                goto err_fd;
        }

        if (group_fd != -1) {
                group_leader = perf_fget_light(group_fd, &fput_needed);
                if (IS_ERR(group_leader)) {
                        err = PTR_ERR(group_leader);
                        goto err_put_context;
                }
                group_file = group_leader->filp;
                if (flags & PERF_FLAG_FD_OUTPUT)
                        output_event = group_leader;
                if (flags & PERF_FLAG_FD_NO_GROUP)
                        group_leader = NULL;
        }

        /*
         * Look up the group leader (we will attach this event to it):
         */
        if (group_leader) {
                err = -EINVAL;

                /*
                 * Do not allow a recursive hierarchy (this new sibling
                 * becoming part of another group-sibling):
                 */
                if (group_leader->group_leader != group_leader)
                        goto err_put_context;
                /*
                 * Do not allow to attach to a group in a different
                 * task or CPU context:
                 */
                if (group_leader->ctx != ctx)
                        goto err_put_context;
                /*
                 * Only a group leader can be exclusive or pinned
                 */
                if (attr.exclusive || attr.pinned)
                        goto err_put_context;
        }

        event = perf_event_alloc(&attr, cpu, ctx, group_leader,
                                     NULL, NULL, GFP_KERNEL);
        if (IS_ERR(event)) {
                err = PTR_ERR(event);
                goto err_put_context;
        }

        if (output_event) {
                err = perf_event_set_output(event, output_event);
                if (err)
                        goto err_free_put_context;
        }

        event_file = anon_inode_getfile("[perf_event]", &perf_fops, event, O_RDWR);
        if (IS_ERR(event_file)) {
                err = PTR_ERR(event_file);
                goto err_free_put_context;
        }

        event->filp = event_file;
        WARN_ON_ONCE(ctx->parent_ctx);
        mutex_lock(&ctx->mutex);
        perf_install_in_context(ctx, event, cpu);
        ++ctx->generation;
        mutex_unlock(&ctx->mutex);

        event->owner = current;
        get_task_struct(current);
        mutex_lock(&current->perf_event_mutex);
        list_add_tail(&event->owner_entry, &current->perf_event_list);
        mutex_unlock(&current->perf_event_mutex);

        /*
         * Drop the reference on the group_event after placing the
         * new event on the sibling_list. This ensures destruction
         * of the group leader will find the pointer to itself in
         * perf_group_detach().
         */
        fput_light(group_file, fput_needed);
        fd_install(event_fd, event_file);
        return event_fd;

err_free_put_context:
        free_event(event);
err_put_context:
        fput_light(group_file, fput_needed);
        put_ctx(ctx);
err_fd:
        put_unused_fd(event_fd);
        return err;
}

/**
 * perf_event_create_kernel_counter
 *
 * @attr: attributes of the counter to create
 * @cpu: cpu in which the counter is bound
 * @pid: task to profile
 */
struct perf_event *
perf_event_create_kernel_counter(struct perf_event_attr *attr, int cpu,
                                 pid_t pid,
                                 perf_overflow_handler_t overflow_handler)
{
        struct perf_event *event;
        struct perf_event_context *ctx;
        int err;

        /*
         * Get the target context (task or percpu):
         */

        ctx = find_get_context(pid, cpu);
        if (IS_ERR(ctx)) {
                err = PTR_ERR(ctx);
                goto err_exit;
        }

        event = perf_event_alloc(attr, cpu, ctx, NULL,
                                 NULL, overflow_handler, GFP_KERNEL);
        if (IS_ERR(event)) {
                err = PTR_ERR(event);
                goto err_put_context;
        }

        event->filp = NULL;
        WARN_ON_ONCE(ctx->parent_ctx);
        mutex_lock(&ctx->mutex);
        perf_install_in_context(ctx, event, cpu);
        ++ctx->generation;
        mutex_unlock(&ctx->mutex);

        event->owner = current;
        get_task_struct(current);
        mutex_lock(&current->perf_event_mutex);
        list_add_tail(&event->owner_entry, &current->perf_event_list);
        mutex_unlock(&current->perf_event_mutex);

        return event;

 err_put_context:
        put_ctx(ctx);
 err_exit:
        return ERR_PTR(err);
}
EXPORT_SYMBOL_GPL(perf_event_create_kernel_counter);

/*
 * inherit a event from parent task to child task:
 */
static struct perf_event *
inherit_event(struct perf_event *parent_event,
              struct task_struct *parent,
              struct perf_event_context *parent_ctx,
              struct task_struct *child,
              struct perf_event *group_leader,
              struct perf_event_context *child_ctx)
{
        struct perf_event *child_event;

        /*
         * Instead of creating recursive hierarchies of events,
         * we link inherited events back to the original parent,
         * which has a filp for sure, which we use as the reference
         * count:
         */
        if (parent_event->parent)
                parent_event = parent_event->parent;

        child_event = perf_event_alloc(&parent_event->attr,
                                           parent_event->cpu, child_ctx,
                                           group_leader, parent_event,
                                           NULL, GFP_KERNEL);
        if (IS_ERR(child_event))
                return child_event;
        get_ctx(child_ctx);

        /*
         * Make the child state follow the state of the parent event,
         * not its attr.disabled bit.  We hold the parent's mutex,
         * so we won't race with perf_event_{en, dis}able_family.
         */
        if (parent_event->state >= PERF_EVENT_STATE_INACTIVE)
                child_event->state = PERF_EVENT_STATE_INACTIVE;
        else
                child_event->state = PERF_EVENT_STATE_OFF;

        if (parent_event->attr.freq) {
                u64 sample_period = parent_event->hw.sample_period;
                struct hw_perf_event *hwc = &child_event->hw;

                hwc->sample_period = sample_period;
                hwc->last_period   = sample_period;

                local64_set(&hwc->period_left, sample_period);
        }

        child_event->overflow_handler = parent_event->overflow_handler;

        /*
         * Link it up in the child's context:
         */
        add_event_to_ctx(child_event, child_ctx);

        /*
         * Get a reference to the parent filp - we will fput it
         * when the child event exits. This is safe to do because
         * we are in the parent and we know that the filp still
         * exists and has a nonzero count:
         */
        atomic_long_inc(&parent_event->filp->f_count);

        /*
         * Link this into the parent event's child list
         */
        WARN_ON_ONCE(parent_event->ctx->parent_ctx);
        mutex_lock(&parent_event->child_mutex);
        list_add_tail(&child_event->child_list, &parent_event->child_list);
        mutex_unlock(&parent_event->child_mutex);

        return child_event;
}

static int inherit_group(struct perf_event *parent_event,
              struct task_struct *parent,
              struct perf_event_context *parent_ctx,
              struct task_struct *child,
              struct perf_event_context *child_ctx)
{
        struct perf_event *leader;
        struct perf_event *sub;
        struct perf_event *child_ctr;

        leader = inherit_event(parent_event, parent, parent_ctx,
                                 child, NULL, child_ctx);
        if (IS_ERR(leader))
                return PTR_ERR(leader);
        list_for_each_entry(sub, &parent_event->sibling_list, group_entry) {
                child_ctr = inherit_event(sub, parent, parent_ctx,
                                            child, leader, child_ctx);
                if (IS_ERR(child_ctr))
                        return PTR_ERR(child_ctr);
        }
        return 0;
}

static void sync_child_event(struct perf_event *child_event,
                               struct task_struct *child)
{
        struct perf_event *parent_event = child_event->parent;
        u64 child_val;

        if (child_event->attr.inherit_stat)
                perf_event_read_event(child_event, child);

        child_val = perf_event_count(child_event);

        /*
         * Add back the child's count to the parent's count:
         */
        atomic64_add(child_val, &parent_event->child_count);
        atomic64_add(child_event->total_time_enabled,
                     &parent_event->child_total_time_enabled);
        atomic64_add(child_event->total_time_running,
                     &parent_event->child_total_time_running);

        /*
         * Remove this event from the parent's list
         */
        WARN_ON_ONCE(parent_event->ctx->parent_ctx);
        mutex_lock(&parent_event->child_mutex);
        list_del_init(&child_event->child_list);
        mutex_unlock(&parent_event->child_mutex);

        /*
         * Release the parent event, if this was the last
         * reference to it.
         */
        fput(parent_event->filp);
}

static void
__perf_event_exit_task(struct perf_event *child_event,
                         struct perf_event_context *child_ctx,
                         struct task_struct *child)
{
        struct perf_event *parent_event;

        perf_event_remove_from_context(child_event);

        parent_event = child_event->parent;
        /*
         * It can happen that parent exits first, and has events
         * that are still around due to the child reference. These
         * events need to be zapped - but otherwise linger.
         */
        if (parent_event) {
                sync_child_event(child_event, child);
                free_event(child_event);
        }
}

/*
 * When a child task exits, feed back event values to parent events.
 */
void perf_event_exit_task(struct task_struct *child)
{
        struct perf_event *child_event, *tmp;
        struct perf_event_context *child_ctx;
        unsigned long flags;

        if (likely(!child->perf_event_ctxp)) {
                perf_event_task(child, NULL, 0);
                return;
        }

        local_irq_save(flags);
        /*
         * We can't reschedule here because interrupts are disabled,
         * and either child is current or it is a task that can't be
         * scheduled, so we are now safe from rescheduling changing
         * our context.
         */
        child_ctx = child->perf_event_ctxp;
        __perf_event_task_sched_out(child_ctx);

        /*
         * Take the context lock here so that if find_get_context is
         * reading child->perf_event_ctxp, we wait until it has
         * incremented the context's refcount before we do put_ctx below.
         */
        raw_spin_lock(&child_ctx->lock);
        child->perf_event_ctxp = NULL;
        /*
         * If this context is a clone; unclone it so it can't get
         * swapped to another process while we're removing all
         * the events from it.
         */
        unclone_ctx(child_ctx);
        update_context_time(child_ctx);
        raw_spin_unlock_irqrestore(&child_ctx->lock, flags);

        /*
         * Report the task dead after unscheduling the events so that we
         * won't get any samples after PERF_RECORD_EXIT. We can however still
         * get a few PERF_RECORD_READ events.
         */
        perf_event_task(child, child_ctx, 0);

        /*
         * We can recurse on the same lock type through:
         *
         *   __perf_event_exit_task()
         *     sync_child_event()
         *       fput(parent_event->filp)
         *         perf_release()
         *           mutex_lock(&ctx->mutex)
         *
         * But since its the parent context it won't be the same instance.
         */
        mutex_lock(&child_ctx->mutex);

again:
        list_for_each_entry_safe(child_event, tmp, &child_ctx->pinned_groups,
                                 group_entry)
                __perf_event_exit_task(child_event, child_ctx, child);

        list_for_each_entry_safe(child_event, tmp, &child_ctx->flexible_groups,
                                 group_entry)
                __perf_event_exit_task(child_event, child_ctx, child);

        /*
         * If the last event was a group event, it will have appended all
         * its siblings to the list, but we obtained 'tmp' before that which
         * will still point to the list head terminating the iteration.
         */
        if (!list_empty(&child_ctx->pinned_groups) ||
            !list_empty(&child_ctx->flexible_groups))
                goto again;

        mutex_unlock(&child_ctx->mutex);

        put_ctx(child_ctx);
}

static void perf_free_event(struct perf_event *event,
                            struct perf_event_context *ctx)
{
        struct perf_event *parent = event->parent;

        if (WARN_ON_ONCE(!parent))
                return;

        mutex_lock(&parent->child_mutex);
        list_del_init(&event->child_list);
        mutex_unlock(&parent->child_mutex);

        fput(parent->filp);

        perf_group_detach(event);
        list_del_event(event, ctx);
        free_event(event);
}

/*
 * free an unexposed, unused context as created by inheritance by
 * init_task below, used by fork() in case of fail.
 */
void perf_event_free_task(struct task_struct *task)
{
        struct perf_event_context *ctx = task->perf_event_ctxp;
        struct perf_event *event, *tmp;

        if (!ctx)
                return;

        mutex_lock(&ctx->mutex);
again:
        list_for_each_entry_safe(event, tmp, &ctx->pinned_groups, group_entry)
                perf_free_event(event, ctx);

        list_for_each_entry_safe(event, tmp, &ctx->flexible_groups,
                                 group_entry)
                perf_free_event(event, ctx);

        if (!list_empty(&ctx->pinned_groups) ||
            !list_empty(&ctx->flexible_groups))
                goto again;

        mutex_unlock(&ctx->mutex);

        put_ctx(ctx);
}

static int
inherit_task_group(struct perf_event *event, struct task_struct *parent,
                   struct perf_event_context *parent_ctx,
                   struct task_struct *child,
                   int *inherited_all)
{
        int ret;
        struct perf_event_context *child_ctx = child->perf_event_ctxp;

        if (!event->attr.inherit) {
                *inherited_all = 0;
                return 0;
        }

        if (!child_ctx) {
                /*
                 * This is executed from the parent task context, so
                 * inherit events that have been marked for cloning.
                 * First allocate and initialize a context for the
                 * child.
                 */

                child_ctx = kzalloc(sizeof(struct perf_event_context),
                                    GFP_KERNEL);
                if (!child_ctx)
                        return -ENOMEM;

                __perf_event_init_context(child_ctx, child);
                child->perf_event_ctxp = child_ctx;
                get_task_struct(child);
        }

        ret = inherit_group(event, parent, parent_ctx,
                            child, child_ctx);

        if (ret)
                *inherited_all = 0;

        return ret;
}


/*
 * Initialize the perf_event context in task_struct
 */
int perf_event_init_task(struct task_struct *child)
{
        struct perf_event_context *child_ctx, *parent_ctx;
        struct perf_event_context *cloned_ctx;
        struct perf_event *event;
        struct task_struct *parent = current;
        int inherited_all = 1;
        int ret = 0;

        child->perf_event_ctxp = NULL;

        mutex_init(&child->perf_event_mutex);
        INIT_LIST_HEAD(&child->perf_event_list);

        if (likely(!parent->perf_event_ctxp))
                return 0;

        /*
         * If the parent's context is a clone, pin it so it won't get
         * swapped under us.
         */
        parent_ctx = perf_pin_task_context(parent);

        /*
         * No need to check if parent_ctx != NULL here; since we saw
         * it non-NULL earlier, the only reason for it to become NULL
         * is if we exit, and since we're currently in the middle of
         * a fork we can't be exiting at the same time.
         */

        /*
         * Lock the parent list. No need to lock the child - not PID
         * hashed yet and not running, so nobody can access it.
         */
        mutex_lock(&parent_ctx->mutex);

        /*
         * We dont have to disable NMIs - we are only looking at
         * the list, not manipulating it:
         */
        list_for_each_entry(event, &parent_ctx->pinned_groups, group_entry) {
                ret = inherit_task_group(event, parent, parent_ctx, child,
                                         &inherited_all);
                if (ret)
                        break;
        }

        list_for_each_entry(event, &parent_ctx->flexible_groups, group_entry) {
                ret = inherit_task_group(event, parent, parent_ctx, child,
                                         &inherited_all);
                if (ret)
                        break;
        }

        child_ctx = child->perf_event_ctxp;

        if (child_ctx && inherited_all) {
                /*
                 * Mark the child context as a clone of the parent
                 * context, or of whatever the parent is a clone of.
                 * Note that if the parent is a clone, it could get
                 * uncloned at any point, but that doesn't matter
                 * because the list of events and the generation
                 * count can't have changed since we took the mutex.
                 */
                cloned_ctx = rcu_dereference(parent_ctx->parent_ctx);
                if (cloned_ctx) {
                        child_ctx->parent_ctx = cloned_ctx;
                        child_ctx->parent_gen = parent_ctx->parent_gen;
                } else {
                        child_ctx->parent_ctx = parent_ctx;
                        child_ctx->parent_gen = parent_ctx->generation;
                }
                get_ctx(child_ctx->parent_ctx);
        }

        mutex_unlock(&parent_ctx->mutex);

        perf_unpin_context(parent_ctx);

        return ret;
}

static void __init perf_event_init_all_cpus(void)
{
        int cpu;
        struct perf_cpu_context *cpuctx;

        for_each_possible_cpu(cpu) {
                cpuctx = &per_cpu(perf_cpu_context, cpu);
                mutex_init(&cpuctx->hlist_mutex);
                __perf_event_init_context(&cpuctx->ctx, NULL);
        }
}

static void __cpuinit perf_event_init_cpu(int cpu)
{
        struct perf_cpu_context *cpuctx;

        cpuctx = &per_cpu(perf_cpu_context, cpu);

        spin_lock(&perf_resource_lock);
        cpuctx->max_pertask = perf_max_events - perf_reserved_percpu;
        spin_unlock(&perf_resource_lock);

        mutex_lock(&cpuctx->hlist_mutex);
        if (cpuctx->hlist_refcount > 0) {
                struct swevent_hlist *hlist;

                hlist = kzalloc(sizeof(*hlist), GFP_KERNEL);
                WARN_ON_ONCE(!hlist);
                rcu_assign_pointer(cpuctx->swevent_hlist, hlist);
        }
        mutex_unlock(&cpuctx->hlist_mutex);
}

#ifdef CONFIG_HOTPLUG_CPU
static void __perf_event_exit_cpu(void *info)
{
        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
        struct perf_event_context *ctx = &cpuctx->ctx;
        struct perf_event *event, *tmp;

        list_for_each_entry_safe(event, tmp, &ctx->pinned_groups, group_entry)
                __perf_event_remove_from_context(event);
        list_for_each_entry_safe(event, tmp, &ctx->flexible_groups, group_entry)
                __perf_event_remove_from_context(event);
}
static void perf_event_exit_cpu(int cpu)
{
        struct perf_cpu_context *cpuctx = &per_cpu(perf_cpu_context, cpu);
        struct perf_event_context *ctx = &cpuctx->ctx;

        mutex_lock(&cpuctx->hlist_mutex);
        swevent_hlist_release(cpuctx);
        mutex_unlock(&cpuctx->hlist_mutex);

        mutex_lock(&ctx->mutex);
        smp_call_function_single(cpu, __perf_event_exit_cpu, NULL, 1);
        mutex_unlock(&ctx->mutex);
}
#else
static inline void perf_event_exit_cpu(int cpu) { }
#endif

static int __cpuinit
perf_cpu_notify(struct notifier_block *self, unsigned long action, void *hcpu)
{
        unsigned int cpu = (long)hcpu;

        switch (action & ~CPU_TASKS_FROZEN) {

        case CPU_UP_PREPARE:
        case CPU_DOWN_FAILED:
                perf_event_init_cpu(cpu);
                break;

        case CPU_UP_CANCELED:
        case CPU_DOWN_PREPARE:
                perf_event_exit_cpu(cpu);
                break;

        default:
                break;
        }

        return NOTIFY_OK;
}

/*
 * This has to have a higher priority than migration_notifier in sched.c.
 */
static struct notifier_block __cpuinitdata perf_cpu_nb = {
        .notifier_call          = perf_cpu_notify,
        .priority               = 20,
};

void __init perf_event_init(void)
{
        perf_event_init_all_cpus();
        perf_cpu_notify(&perf_cpu_nb, (unsigned long)CPU_UP_PREPARE,
                        (void *)(long)smp_processor_id());
        perf_cpu_notify(&perf_cpu_nb, (unsigned long)CPU_ONLINE,
                        (void *)(long)smp_processor_id());
        register_cpu_notifier(&perf_cpu_nb);
}

static ssize_t perf_show_reserve_percpu(struct sysdev_class *class,
                                        struct sysdev_class_attribute *attr,
                                        char *buf)
{
        return sprintf(buf, "%d\n", perf_reserved_percpu);
}

static ssize_t
perf_set_reserve_percpu(struct sysdev_class *class,
                        struct sysdev_class_attribute *attr,
                        const char *buf,
                        size_t count)
{
        struct perf_cpu_context *cpuctx;
        unsigned long val;
        int err, cpu, mpt;

        err = strict_strtoul(buf, 10, &val);
        if (err)
                return err;
        if (val > perf_max_events)
                return -EINVAL;

        spin_lock(&perf_resource_lock);
        perf_reserved_percpu = val;
        for_each_online_cpu(cpu) {
                cpuctx = &per_cpu(perf_cpu_context, cpu);
                raw_spin_lock_irq(&cpuctx->ctx.lock);
                mpt = min(perf_max_events - cpuctx->ctx.nr_events,
                          perf_max_events - perf_reserved_percpu);
                cpuctx->max_pertask = mpt;
                raw_spin_unlock_irq(&cpuctx->ctx.lock);
        }
        spin_unlock(&perf_resource_lock);

        return count;
}

static ssize_t perf_show_overcommit(struct sysdev_class *class,
                                    struct sysdev_class_attribute *attr,
                                    char *buf)
{
        return sprintf(buf, "%d\n", perf_overcommit);
}

static ssize_t
perf_set_overcommit(struct sysdev_class *class,
                    struct sysdev_class_attribute *attr,
                    const char *buf, size_t count)
{
        unsigned long val;
        int err;

        err = strict_strtoul(buf, 10, &val);
        if (err)
                return err;
        if (val > 1)
                return -EINVAL;

        spin_lock(&perf_resource_lock);
        perf_overcommit = val;
        spin_unlock(&perf_resource_lock);

        return count;
}

static SYSDEV_CLASS_ATTR(
                                reserve_percpu,
                                0644,
                                perf_show_reserve_percpu,
                                perf_set_reserve_percpu
                        );

static SYSDEV_CLASS_ATTR(
                                overcommit,
                                0644,
                                perf_show_overcommit,
                                perf_set_overcommit
                        );

static struct attribute *perfclass_attrs[] = {
        &attr_reserve_percpu.attr,
        &attr_overcommit.attr,
        NULL
};

static struct attribute_group perfclass_attr_group = {
        .attrs                  = perfclass_attrs,
        .name                   = "perf_events",
};

static int __init perf_event_sysfs_init(void)
{
        return sysfs_create_group(&cpu_sysdev_class.kset.kobj,
                                  &perfclass_attr_group);
}
device_initcall(perf_event_sysfs_init);