powerpc/kexec: Fix orphaned offline CPUs across kexec

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

/*
 *  kernel/cpuset.c
 *
 *  Processor and Memory placement constraints for sets of tasks.
 *
 *  Copyright (C) 2003 BULL SA.
 *  Copyright (C) 2004-2007 Silicon Graphics, Inc.
 *  Copyright (C) 2006 Google, Inc
 *
 *  Portions derived from Patrick Mochel's sysfs code.
 *  sysfs is Copyright (c) 2001-3 Patrick Mochel
 *
 *  2003-10-10 Written by Simon Derr.
 *  2003-10-22 Updates by Stephen Hemminger.
 *  2004 May-July Rework by Paul Jackson.
 *  2006 Rework by Paul Menage to use generic cgroups
 *  2008 Rework of the scheduler domains and CPU hotplug handling
 *       by Max Krasnyansky
 *
 *  This file is subject to the terms and conditions of the GNU General Public
 *  License.  See the file COPYING in the main directory of the Linux
 *  distribution for more details.
 */

#include <linux/cpu.h>
#include <linux/cpumask.h>
#include <linux/cpuset.h>
#include <linux/err.h>
#include <linux/errno.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/kernel.h>
#include <linux/kmod.h>
#include <linux/list.h>
#include <linux/mempolicy.h>
#include <linux/mm.h>
#include <linux/memory.h>
#include <linux/module.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/pagemap.h>
#include <linux/proc_fs.h>
#include <linux/rcupdate.h>
#include <linux/sched.h>
#include <linux/seq_file.h>
#include <linux/security.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/stat.h>
#include <linux/string.h>
#include <linux/time.h>
#include <linux/backing-dev.h>
#include <linux/sort.h>

#include <asm/uaccess.h>
#include <asm/atomic.h>
#include <linux/mutex.h>
#include <linux/workqueue.h>
#include <linux/cgroup.h>

/*
 * Workqueue for cpuset related tasks.
 *
 * Using kevent workqueue may cause deadlock when memory_migrate
 * is set. So we create a separate workqueue thread for cpuset.
 */
static struct workqueue_struct *cpuset_wq;

/*
 * Tracks how many cpusets are currently defined in system.
 * When there is only one cpuset (the root cpuset) we can
 * short circuit some hooks.
 */
int number_of_cpusets __read_mostly;

/* Forward declare cgroup structures */
struct cgroup_subsys cpuset_subsys;
struct cpuset;

/* See "Frequency meter" comments, below. */

struct fmeter {
        int cnt;                /* unprocessed events count */
        int val;                /* most recent output value */
        time_t time;            /* clock (secs) when val computed */
        spinlock_t lock;        /* guards read or write of above */
};

struct cpuset {
        struct cgroup_subsys_state css;

        unsigned long flags;            /* "unsigned long" so bitops work */
        cpumask_var_t cpus_allowed;     /* CPUs allowed to tasks in cpuset */
        nodemask_t mems_allowed;        /* Memory Nodes allowed to tasks */

        struct cpuset *parent;          /* my parent */

        struct fmeter fmeter;           /* memory_pressure filter */

        /* partition number for rebuild_sched_domains() */
        int pn;

        /* for custom sched domain */
        int relax_domain_level;

        /* used for walking a cpuset heirarchy */
        struct list_head stack_list;
};

/* Retrieve the cpuset for a cgroup */
static inline struct cpuset *cgroup_cs(struct cgroup *cont)
{
        return container_of(cgroup_subsys_state(cont, cpuset_subsys_id),
                            struct cpuset, css);
}

/* Retrieve the cpuset for a task */
static inline struct cpuset *task_cs(struct task_struct *task)
{
        return container_of(task_subsys_state(task, cpuset_subsys_id),
                            struct cpuset, css);
}

/* bits in struct cpuset flags field */
typedef enum {
        CS_CPU_EXCLUSIVE,
        CS_MEM_EXCLUSIVE,
        CS_MEM_HARDWALL,
        CS_MEMORY_MIGRATE,
        CS_SCHED_LOAD_BALANCE,
        CS_SPREAD_PAGE,
        CS_SPREAD_SLAB,
} cpuset_flagbits_t;

/* convenient tests for these bits */
static inline int is_cpu_exclusive(const struct cpuset *cs)
{
        return test_bit(CS_CPU_EXCLUSIVE, &cs->flags);
}

static inline int is_mem_exclusive(const struct cpuset *cs)
{
        return test_bit(CS_MEM_EXCLUSIVE, &cs->flags);
}

static inline int is_mem_hardwall(const struct cpuset *cs)
{
        return test_bit(CS_MEM_HARDWALL, &cs->flags);
}

static inline int is_sched_load_balance(const struct cpuset *cs)
{
        return test_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
}

static inline int is_memory_migrate(const struct cpuset *cs)
{
        return test_bit(CS_MEMORY_MIGRATE, &cs->flags);
}

static inline int is_spread_page(const struct cpuset *cs)
{
        return test_bit(CS_SPREAD_PAGE, &cs->flags);
}

static inline int is_spread_slab(const struct cpuset *cs)
{
        return test_bit(CS_SPREAD_SLAB, &cs->flags);
}

static struct cpuset top_cpuset = {
        .flags = ((1 << CS_CPU_EXCLUSIVE) | (1 << CS_MEM_EXCLUSIVE)),
};

/*
 * There are two global mutexes guarding cpuset structures.  The first
 * is the main control groups cgroup_mutex, accessed via
 * cgroup_lock()/cgroup_unlock().  The second is the cpuset-specific
 * callback_mutex, below. They can nest.  It is ok to first take
 * cgroup_mutex, then nest callback_mutex.  We also require taking
 * task_lock() when dereferencing a task's cpuset pointer.  See "The
 * task_lock() exception", at the end of this comment.
 *
 * A task must hold both mutexes to modify cpusets.  If a task
 * holds cgroup_mutex, then it blocks others wanting that mutex,
 * ensuring that it is the only task able to also acquire callback_mutex
 * and be able to modify cpusets.  It can perform various checks on
 * the cpuset structure first, knowing nothing will change.  It can
 * also allocate memory while just holding cgroup_mutex.  While it is
 * performing these checks, various callback routines can briefly
 * acquire callback_mutex to query cpusets.  Once it is ready to make
 * the changes, it takes callback_mutex, blocking everyone else.
 *
 * Calls to the kernel memory allocator can not be made while holding
 * callback_mutex, as that would risk double tripping on callback_mutex
 * from one of the callbacks into the cpuset code from within
 * __alloc_pages().
 *
 * If a task is only holding callback_mutex, then it has read-only
 * access to cpusets.
 *
 * Now, the task_struct fields mems_allowed and mempolicy may be changed
 * by other task, we use alloc_lock in the task_struct fields to protect
 * them.
 *
 * The cpuset_common_file_read() handlers only hold callback_mutex across
 * small pieces of code, such as when reading out possibly multi-word
 * cpumasks and nodemasks.
 *
 * Accessing a task's cpuset should be done in accordance with the
 * guidelines for accessing subsystem state in kernel/cgroup.c
 */

static DEFINE_MUTEX(callback_mutex);

/*
 * cpuset_buffer_lock protects both the cpuset_name and cpuset_nodelist
 * buffers.  They are statically allocated to prevent using excess stack
 * when calling cpuset_print_task_mems_allowed().
 */
#define CPUSET_NAME_LEN         (128)
#define CPUSET_NODELIST_LEN     (256)
static char cpuset_name[CPUSET_NAME_LEN];
static char cpuset_nodelist[CPUSET_NODELIST_LEN];
static DEFINE_SPINLOCK(cpuset_buffer_lock);

/*
 * This is ugly, but preserves the userspace API for existing cpuset
 * users. If someone tries to mount the "cpuset" filesystem, we
 * silently switch it to mount "cgroup" instead
 */
static int cpuset_get_sb(struct file_system_type *fs_type,
                         int flags, const char *unused_dev_name,
                         void *data, struct vfsmount *mnt)
{
        struct file_system_type *cgroup_fs = get_fs_type("cgroup");
        int ret = -ENODEV;
        if (cgroup_fs) {
                char mountopts[] =
                        "cpuset,noprefix,"
                        "release_agent=/sbin/cpuset_release_agent";
                ret = cgroup_fs->get_sb(cgroup_fs, flags,
                                           unused_dev_name, mountopts, mnt);
                put_filesystem(cgroup_fs);
        }
        return ret;
}

static struct file_system_type cpuset_fs_type = {
        .name = "cpuset",
        .get_sb = cpuset_get_sb,
};

/*
 * Return in pmask the portion of a cpusets's cpus_allowed that
 * are online.  If none are online, walk up the cpuset hierarchy
 * until we find one that does have some online cpus.  If we get
 * all the way to the top and still haven't found any online cpus,
 * return cpu_online_map.  Or if passed a NULL cs from an exit'ing
 * task, return cpu_online_map.
 *
 * One way or another, we guarantee to return some non-empty subset
 * of cpu_online_map.
 *
 * Call with callback_mutex held.
 */

static void guarantee_online_cpus(const struct cpuset *cs,
                                  struct cpumask *pmask)
{
        while (cs && !cpumask_intersects(cs->cpus_allowed, cpu_online_mask))
                cs = cs->parent;
        if (cs)
                cpumask_and(pmask, cs->cpus_allowed, cpu_online_mask);
        else
                cpumask_copy(pmask, cpu_online_mask);
        BUG_ON(!cpumask_intersects(pmask, cpu_online_mask));
}

/*
 * Return in *pmask the portion of a cpusets's mems_allowed that
 * are online, with memory.  If none are online with memory, walk
 * up the cpuset hierarchy until we find one that does have some
 * online mems.  If we get all the way to the top and still haven't
 * found any online mems, return node_states[N_HIGH_MEMORY].
 *
 * One way or another, we guarantee to return some non-empty subset
 * of node_states[N_HIGH_MEMORY].
 *
 * Call with callback_mutex held.
 */

static void guarantee_online_mems(const struct cpuset *cs, nodemask_t *pmask)
{
        while (cs && !nodes_intersects(cs->mems_allowed,
                                        node_states[N_HIGH_MEMORY]))
                cs = cs->parent;
        if (cs)
                nodes_and(*pmask, cs->mems_allowed,
                                        node_states[N_HIGH_MEMORY]);
        else
                *pmask = node_states[N_HIGH_MEMORY];
        BUG_ON(!nodes_intersects(*pmask, node_states[N_HIGH_MEMORY]));
}

/*
 * update task's spread flag if cpuset's page/slab spread flag is set
 *
 * Called with callback_mutex/cgroup_mutex held
 */
static void cpuset_update_task_spread_flag(struct cpuset *cs,
                                        struct task_struct *tsk)
{
        if (is_spread_page(cs))
                tsk->flags |= PF_SPREAD_PAGE;
        else
                tsk->flags &= ~PF_SPREAD_PAGE;
        if (is_spread_slab(cs))
                tsk->flags |= PF_SPREAD_SLAB;
        else
                tsk->flags &= ~PF_SPREAD_SLAB;
}

/*
 * is_cpuset_subset(p, q) - Is cpuset p a subset of cpuset q?
 *
 * One cpuset is a subset of another if all its allowed CPUs and
 * Memory Nodes are a subset of the other, and its exclusive flags
 * are only set if the other's are set.  Call holding cgroup_mutex.
 */

static int is_cpuset_subset(const struct cpuset *p, const struct cpuset *q)
{
        return  cpumask_subset(p->cpus_allowed, q->cpus_allowed) &&
                nodes_subset(p->mems_allowed, q->mems_allowed) &&
                is_cpu_exclusive(p) <= is_cpu_exclusive(q) &&
                is_mem_exclusive(p) <= is_mem_exclusive(q);
}

/**
 * alloc_trial_cpuset - allocate a trial cpuset
 * @cs: the cpuset that the trial cpuset duplicates
 */
static struct cpuset *alloc_trial_cpuset(const struct cpuset *cs)
{
        struct cpuset *trial;

        trial = kmemdup(cs, sizeof(*cs), GFP_KERNEL);
        if (!trial)
                return NULL;

        if (!alloc_cpumask_var(&trial->cpus_allowed, GFP_KERNEL)) {
                kfree(trial);
                return NULL;
        }
        cpumask_copy(trial->cpus_allowed, cs->cpus_allowed);

        return trial;
}

/**
 * free_trial_cpuset - free the trial cpuset
 * @trial: the trial cpuset to be freed
 */
static void free_trial_cpuset(struct cpuset *trial)
{
        free_cpumask_var(trial->cpus_allowed);
        kfree(trial);
}

/*
 * validate_change() - Used to validate that any proposed cpuset change
 *                     follows the structural rules for cpusets.
 *
 * If we replaced the flag and mask values of the current cpuset
 * (cur) with those values in the trial cpuset (trial), would
 * our various subset and exclusive rules still be valid?  Presumes
 * cgroup_mutex held.
 *
 * 'cur' is the address of an actual, in-use cpuset.  Operations
 * such as list traversal that depend on the actual address of the
 * cpuset in the list must use cur below, not trial.
 *
 * 'trial' is the address of bulk structure copy of cur, with
 * perhaps one or more of the fields cpus_allowed, mems_allowed,
 * or flags changed to new, trial values.
 *
 * Return 0 if valid, -errno if not.
 */

static int validate_change(const struct cpuset *cur, const struct cpuset *trial)
{
        struct cgroup *cont;
        struct cpuset *c, *par;

        /* Each of our child cpusets must be a subset of us */
        list_for_each_entry(cont, &cur->css.cgroup->children, sibling) {
                if (!is_cpuset_subset(cgroup_cs(cont), trial))
                        return -EBUSY;
        }

        /* Remaining checks don't apply to root cpuset */
        if (cur == &top_cpuset)
                return 0;

        par = cur->parent;

        /* We must be a subset of our parent cpuset */
        if (!is_cpuset_subset(trial, par))
                return -EACCES;

        /*
         * If either I or some sibling (!= me) is exclusive, we can't
         * overlap
         */
        list_for_each_entry(cont, &par->css.cgroup->children, sibling) {
                c = cgroup_cs(cont);
                if ((is_cpu_exclusive(trial) || is_cpu_exclusive(c)) &&
                    c != cur &&
                    cpumask_intersects(trial->cpus_allowed, c->cpus_allowed))
                        return -EINVAL;
                if ((is_mem_exclusive(trial) || is_mem_exclusive(c)) &&
                    c != cur &&
                    nodes_intersects(trial->mems_allowed, c->mems_allowed))
                        return -EINVAL;
        }

        /* Cpusets with tasks can't have empty cpus_allowed or mems_allowed */
        if (cgroup_task_count(cur->css.cgroup)) {
                if (cpumask_empty(trial->cpus_allowed) ||
                    nodes_empty(trial->mems_allowed)) {
                        return -ENOSPC;
                }
        }

        return 0;
}

#ifdef CONFIG_SMP
/*
 * Helper routine for generate_sched_domains().
 * Do cpusets a, b have overlapping cpus_allowed masks?
 */
static int cpusets_overlap(struct cpuset *a, struct cpuset *b)
{
        return cpumask_intersects(a->cpus_allowed, b->cpus_allowed);
}

static void
update_domain_attr(struct sched_domain_attr *dattr, struct cpuset *c)
{
        if (dattr->relax_domain_level < c->relax_domain_level)
                dattr->relax_domain_level = c->relax_domain_level;
        return;
}

static void
update_domain_attr_tree(struct sched_domain_attr *dattr, struct cpuset *c)
{
        LIST_HEAD(q);

        list_add(&c->stack_list, &q);
        while (!list_empty(&q)) {
                struct cpuset *cp;
                struct cgroup *cont;
                struct cpuset *child;

                cp = list_first_entry(&q, struct cpuset, stack_list);
                list_del(q.next);

                if (cpumask_empty(cp->cpus_allowed))
                        continue;

                if (is_sched_load_balance(cp))
                        update_domain_attr(dattr, cp);

                list_for_each_entry(cont, &cp->css.cgroup->children, sibling) {
                        child = cgroup_cs(cont);
                        list_add_tail(&child->stack_list, &q);
                }
        }
}

/*
 * generate_sched_domains()
 *
 * This function builds a partial partition of the systems CPUs
 * A 'partial partition' is a set of non-overlapping subsets whose
 * union is a subset of that set.
 * The output of this function needs to be passed to kernel/sched.c
 * partition_sched_domains() routine, which will rebuild the scheduler's
 * load balancing domains (sched domains) as specified by that partial
 * partition.
 *
 * See "What is sched_load_balance" in Documentation/cgroups/cpusets.txt
 * for a background explanation of this.
 *
 * Does not return errors, on the theory that the callers of this
 * routine would rather not worry about failures to rebuild sched
 * domains when operating in the severe memory shortage situations
 * that could cause allocation failures below.
 *
 * Must be called with cgroup_lock held.
 *
 * The three key local variables below are:
 *    q  - a linked-list queue of cpuset pointers, used to implement a
 *         top-down scan of all cpusets.  This scan loads a pointer
 *         to each cpuset marked is_sched_load_balance into the
 *         array 'csa'.  For our purposes, rebuilding the schedulers
 *         sched domains, we can ignore !is_sched_load_balance cpusets.
 *  csa  - (for CpuSet Array) Array of pointers to all the cpusets
 *         that need to be load balanced, for convenient iterative
 *         access by the subsequent code that finds the best partition,
 *         i.e the set of domains (subsets) of CPUs such that the
 *         cpus_allowed of every cpuset marked is_sched_load_balance
 *         is a subset of one of these domains, while there are as
 *         many such domains as possible, each as small as possible.
 * doms  - Conversion of 'csa' to an array of cpumasks, for passing to
 *         the kernel/sched.c routine partition_sched_domains() in a
 *         convenient format, that can be easily compared to the prior
 *         value to determine what partition elements (sched domains)
 *         were changed (added or removed.)
 *
 * Finding the best partition (set of domains):
 *      The triple nested loops below over i, j, k scan over the
 *      load balanced cpusets (using the array of cpuset pointers in
 *      csa[]) looking for pairs of cpusets that have overlapping
 *      cpus_allowed, but which don't have the same 'pn' partition
 *      number and gives them in the same partition number.  It keeps
 *      looping on the 'restart' label until it can no longer find
 *      any such pairs.
 *
 *      The union of the cpus_allowed masks from the set of
 *      all cpusets having the same 'pn' value then form the one
 *      element of the partition (one sched domain) to be passed to
 *      partition_sched_domains().
 */
static int generate_sched_domains(cpumask_var_t **domains,
                        struct sched_domain_attr **attributes)
{
        LIST_HEAD(q);           /* queue of cpusets to be scanned */
        struct cpuset *cp;      /* scans q */
        struct cpuset **csa;    /* array of all cpuset ptrs */
        int csn;                /* how many cpuset ptrs in csa so far */
        int i, j, k;            /* indices for partition finding loops */
        cpumask_var_t *doms;    /* resulting partition; i.e. sched domains */
        struct sched_domain_attr *dattr;  /* attributes for custom domains */
        int ndoms = 0;          /* number of sched domains in result */
        int nslot;              /* next empty doms[] struct cpumask slot */

        doms = NULL;
        dattr = NULL;
        csa = NULL;

        /* Special case for the 99% of systems with one, full, sched domain */
        if (is_sched_load_balance(&top_cpuset)) {
                ndoms = 1;
                doms = alloc_sched_domains(ndoms);
                if (!doms)
                        goto done;

                dattr = kmalloc(sizeof(struct sched_domain_attr), GFP_KERNEL);
                if (dattr) {
                        *dattr = SD_ATTR_INIT;
                        update_domain_attr_tree(dattr, &top_cpuset);
                }
                cpumask_copy(doms[0], top_cpuset.cpus_allowed);

                goto done;
        }

        csa = kmalloc(number_of_cpusets * sizeof(cp), GFP_KERNEL);
        if (!csa)
                goto done;
        csn = 0;

        list_add(&top_cpuset.stack_list, &q);
        while (!list_empty(&q)) {
                struct cgroup *cont;
                struct cpuset *child;   /* scans child cpusets of cp */

                cp = list_first_entry(&q, struct cpuset, stack_list);
                list_del(q.next);

                if (cpumask_empty(cp->cpus_allowed))
                        continue;

                /*
                 * All child cpusets contain a subset of the parent's cpus, so
                 * just skip them, and then we call update_domain_attr_tree()
                 * to calc relax_domain_level of the corresponding sched
                 * domain.
                 */
                if (is_sched_load_balance(cp)) {
                        csa[csn++] = cp;
                        continue;
                }

                list_for_each_entry(cont, &cp->css.cgroup->children, sibling) {
                        child = cgroup_cs(cont);
                        list_add_tail(&child->stack_list, &q);
                }
        }

        for (i = 0; i < csn; i++)
                csa[i]->pn = i;
        ndoms = csn;

restart:
        /* Find the best partition (set of sched domains) */
        for (i = 0; i < csn; i++) {
                struct cpuset *a = csa[i];
                int apn = a->pn;

                for (j = 0; j < csn; j++) {
                        struct cpuset *b = csa[j];
                        int bpn = b->pn;

                        if (apn != bpn && cpusets_overlap(a, b)) {
                                for (k = 0; k < csn; k++) {
                                        struct cpuset *c = csa[k];

                                        if (c->pn == bpn)
                                                c->pn = apn;
                                }
                                ndoms--;        /* one less element */
                                goto restart;
                        }
                }
        }

        /*
         * Now we know how many domains to create.
         * Convert <csn, csa> to <ndoms, doms> and populate cpu masks.
         */
        doms = alloc_sched_domains(ndoms);
        if (!doms)
                goto done;

        /*
         * The rest of the code, including the scheduler, can deal with
         * dattr==NULL case. No need to abort if alloc fails.
         */
        dattr = kmalloc(ndoms * sizeof(struct sched_domain_attr), GFP_KERNEL);

        for (nslot = 0, i = 0; i < csn; i++) {
                struct cpuset *a = csa[i];
                struct cpumask *dp;
                int apn = a->pn;

                if (apn < 0) {
                        /* Skip completed partitions */
                        continue;
                }

                dp = doms[nslot];

                if (nslot == ndoms) {
                        static int warnings = 10;
                        if (warnings) {
                                printk(KERN_WARNING
                                 "rebuild_sched_domains confused:"
                                  " nslot %d, ndoms %d, csn %d, i %d,"
                                  " apn %d\n",
                                  nslot, ndoms, csn, i, apn);
                                warnings--;
                        }
                        continue;
                }

                cpumask_clear(dp);
                if (dattr)
                        *(dattr + nslot) = SD_ATTR_INIT;
                for (j = i; j < csn; j++) {
                        struct cpuset *b = csa[j];

                        if (apn == b->pn) {
                                cpumask_or(dp, dp, b->cpus_allowed);
                                if (dattr)
                                        update_domain_attr_tree(dattr + nslot, b);

                                /* Done with this partition */
                                b->pn = -1;
                        }
                }
                nslot++;
        }
        BUG_ON(nslot != ndoms);

done:
        kfree(csa);

        /*
         * Fallback to the default domain if kmalloc() failed.
         * See comments in partition_sched_domains().
         */
        if (doms == NULL)
                ndoms = 1;

        *domains    = doms;
        *attributes = dattr;
        return ndoms;
}

/*
 * Rebuild scheduler domains.
 *
 * Call with neither cgroup_mutex held nor within get_online_cpus().
 * Takes both cgroup_mutex and get_online_cpus().
 *
 * Cannot be directly called from cpuset code handling changes
 * to the cpuset pseudo-filesystem, because it cannot be called
 * from code that already holds cgroup_mutex.
 */
static void do_rebuild_sched_domains(struct work_struct *unused)
{
        struct sched_domain_attr *attr;
        cpumask_var_t *doms;
        int ndoms;

        get_online_cpus();

        /* Generate domain masks and attrs */
        cgroup_lock();
        ndoms = generate_sched_domains(&doms, &attr);
        cgroup_unlock();

        /* Have scheduler rebuild the domains */
        partition_sched_domains(ndoms, doms, attr);

        put_online_cpus();
}
#else /* !CONFIG_SMP */
static void do_rebuild_sched_domains(struct work_struct *unused)
{
}

static int generate_sched_domains(cpumask_var_t **domains,
                        struct sched_domain_attr **attributes)
{
        *domains = NULL;
        return 1;
}
#endif /* CONFIG_SMP */

static DECLARE_WORK(rebuild_sched_domains_work, do_rebuild_sched_domains);

/*
 * Rebuild scheduler domains, asynchronously via workqueue.
 *
 * If the flag 'sched_load_balance' of any cpuset with non-empty
 * 'cpus' changes, or if the 'cpus' allowed changes in any cpuset
 * which has that flag enabled, or if any cpuset with a non-empty
 * 'cpus' is removed, then call this routine to rebuild the
 * scheduler's dynamic sched domains.
 *
 * The rebuild_sched_domains() and partition_sched_domains()
 * routines must nest cgroup_lock() inside get_online_cpus(),
 * but such cpuset changes as these must nest that locking the
 * other way, holding cgroup_lock() for much of the code.
 *
 * So in order to avoid an ABBA deadlock, the cpuset code handling
 * these user changes delegates the actual sched domain rebuilding
 * to a separate workqueue thread, which ends up processing the
 * above do_rebuild_sched_domains() function.
 */
static void async_rebuild_sched_domains(void)
{
        queue_work(cpuset_wq, &rebuild_sched_domains_work);
}

/*
 * Accomplishes the same scheduler domain rebuild as the above
 * async_rebuild_sched_domains(), however it directly calls the
 * rebuild routine synchronously rather than calling it via an
 * asynchronous work thread.
 *
 * This can only be called from code that is not holding
 * cgroup_mutex (not nested in a cgroup_lock() call.)
 */
void rebuild_sched_domains(void)
{
        do_rebuild_sched_domains(NULL);
}

/**
 * cpuset_test_cpumask - test a task's cpus_allowed versus its cpuset's
 * @tsk: task to test
 * @scan: struct cgroup_scanner contained in its struct cpuset_hotplug_scanner
 *
 * Call with cgroup_mutex held.  May take callback_mutex during call.
 * Called for each task in a cgroup by cgroup_scan_tasks().
 * Return nonzero if this tasks's cpus_allowed mask should be changed (in other
 * words, if its mask is not equal to its cpuset's mask).
 */
static int cpuset_test_cpumask(struct task_struct *tsk,
                               struct cgroup_scanner *scan)
{
        return !cpumask_equal(&tsk->cpus_allowed,
                        (cgroup_cs(scan->cg))->cpus_allowed);
}

/**
 * cpuset_change_cpumask - make a task's cpus_allowed the same as its cpuset's
 * @tsk: task to test
 * @scan: struct cgroup_scanner containing the cgroup of the task
 *
 * Called by cgroup_scan_tasks() for each task in a cgroup whose
 * cpus_allowed mask needs to be changed.
 *
 * We don't need to re-check for the cgroup/cpuset membership, since we're
 * holding cgroup_lock() at this point.
 */
static void cpuset_change_cpumask(struct task_struct *tsk,
                                  struct cgroup_scanner *scan)
{
        set_cpus_allowed_ptr(tsk, ((cgroup_cs(scan->cg))->cpus_allowed));
}

/**
 * update_tasks_cpumask - Update the cpumasks of tasks in the cpuset.
 * @cs: the cpuset in which each task's cpus_allowed mask needs to be changed
 * @heap: if NULL, defer allocating heap memory to cgroup_scan_tasks()
 *
 * Called with cgroup_mutex held
 *
 * The cgroup_scan_tasks() function will scan all the tasks in a cgroup,
 * calling callback functions for each.
 *
 * No return value. It's guaranteed that cgroup_scan_tasks() always returns 0
 * if @heap != NULL.
 */
static void update_tasks_cpumask(struct cpuset *cs, struct ptr_heap *heap)
{
        struct cgroup_scanner scan;

        scan.cg = cs->css.cgroup;
        scan.test_task = cpuset_test_cpumask;
        scan.process_task = cpuset_change_cpumask;
        scan.heap = heap;
        cgroup_scan_tasks(&scan);
}

/**
 * update_cpumask - update the cpus_allowed mask of a cpuset and all tasks in it
 * @cs: the cpuset to consider
 * @buf: buffer of cpu numbers written to this cpuset
 */
static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
                          const char *buf)
{
        struct ptr_heap heap;
        int retval;
        int is_load_balanced;

        /* top_cpuset.cpus_allowed tracks cpu_online_map; it's read-only */
        if (cs == &top_cpuset)
                return -EACCES;

        /*
         * An empty cpus_allowed is ok only if the cpuset has no tasks.
         * Since cpulist_parse() fails on an empty mask, we special case
         * that parsing.  The validate_change() call ensures that cpusets
         * with tasks have cpus.
         */
        if (!*buf) {
                cpumask_clear(trialcs->cpus_allowed);
        } else {
                retval = cpulist_parse(buf, trialcs->cpus_allowed);
                if (retval < 0)
                        return retval;

                if (!cpumask_subset(trialcs->cpus_allowed, cpu_active_mask))
                        return -EINVAL;
        }
        retval = validate_change(cs, trialcs);
        if (retval < 0)
                return retval;

        /* Nothing to do if the cpus didn't change */
        if (cpumask_equal(cs->cpus_allowed, trialcs->cpus_allowed))
                return 0;

        retval = heap_init(&heap, PAGE_SIZE, GFP_KERNEL, NULL);
        if (retval)
                return retval;

        is_load_balanced = is_sched_load_balance(trialcs);

        mutex_lock(&callback_mutex);
        cpumask_copy(cs->cpus_allowed, trialcs->cpus_allowed);
        mutex_unlock(&callback_mutex);

        /*
         * Scan tasks in the cpuset, and update the cpumasks of any
         * that need an update.
         */
        update_tasks_cpumask(cs, &heap);

        heap_free(&heap);

        if (is_load_balanced)
                async_rebuild_sched_domains();
        return 0;
}

/*
 * cpuset_migrate_mm
 *
 *    Migrate memory region from one set of nodes to another.
 *
 *    Temporarilly set tasks mems_allowed to target nodes of migration,
 *    so that the migration code can allocate pages on these nodes.
 *
 *    Call holding cgroup_mutex, so current's cpuset won't change
 *    during this call, as manage_mutex holds off any cpuset_attach()
 *    calls.  Therefore we don't need to take task_lock around the
 *    call to guarantee_online_mems(), as we know no one is changing
 *    our task's cpuset.
 *
 *    While the mm_struct we are migrating is typically from some
 *    other task, the task_struct mems_allowed that we are hacking
 *    is for our current task, which must allocate new pages for that
 *    migrating memory region.
 */

static void cpuset_migrate_mm(struct mm_struct *mm, const nodemask_t *from,
                                                        const nodemask_t *to)
{
        struct task_struct *tsk = current;

        tsk->mems_allowed = *to;

        do_migrate_pages(mm, from, to, MPOL_MF_MOVE_ALL);

        guarantee_online_mems(task_cs(tsk),&tsk->mems_allowed);
}

/*
 * cpuset_change_task_nodemask - change task's mems_allowed and mempolicy
 * @tsk: the task to change
 * @newmems: new nodes that the task will be set
 *
 * In order to avoid seeing no nodes if the old and new nodes are disjoint,
 * we structure updates as setting all new allowed nodes, then clearing newly
 * disallowed ones.
 *
 * Called with task's alloc_lock held
 */
static void cpuset_change_task_nodemask(struct task_struct *tsk,
                                        nodemask_t *newmems)
{
        nodes_or(tsk->mems_allowed, tsk->mems_allowed, *newmems);
        mpol_rebind_task(tsk, &tsk->mems_allowed);
        mpol_rebind_task(tsk, newmems);
        tsk->mems_allowed = *newmems;
}

/*
 * Update task's mems_allowed and rebind its mempolicy and vmas' mempolicy
 * of it to cpuset's new mems_allowed, and migrate pages to new nodes if
 * memory_migrate flag is set. Called with cgroup_mutex held.
 */
static void cpuset_change_nodemask(struct task_struct *p,
                                   struct cgroup_scanner *scan)
{
        struct mm_struct *mm;
        struct cpuset *cs;
        int migrate;
        const nodemask_t *oldmem = scan->data;
        nodemask_t newmems;

        cs = cgroup_cs(scan->cg);
        guarantee_online_mems(cs, &newmems);

        task_lock(p);
        cpuset_change_task_nodemask(p, &newmems);
        task_unlock(p);

        mm = get_task_mm(p);
        if (!mm)
                return;

        migrate = is_memory_migrate(cs);

        mpol_rebind_mm(mm, &cs->mems_allowed);
        if (migrate)
                cpuset_migrate_mm(mm, oldmem, &cs->mems_allowed);
        mmput(mm);
}

static void *cpuset_being_rebound;

/**
 * update_tasks_nodemask - Update the nodemasks of tasks in the cpuset.
 * @cs: the cpuset in which each task's mems_allowed mask needs to be changed
 * @oldmem: old mems_allowed of cpuset cs
 * @heap: if NULL, defer allocating heap memory to cgroup_scan_tasks()
 *
 * Called with cgroup_mutex held
 * No return value. It's guaranteed that cgroup_scan_tasks() always returns 0
 * if @heap != NULL.
 */
static void update_tasks_nodemask(struct cpuset *cs, const nodemask_t *oldmem,
                                 struct ptr_heap *heap)
{
        struct cgroup_scanner scan;

        cpuset_being_rebound = cs;              /* causes mpol_dup() rebind */

        scan.cg = cs->css.cgroup;
        scan.test_task = NULL;
        scan.process_task = cpuset_change_nodemask;
        scan.heap = heap;
        scan.data = (nodemask_t *)oldmem;

        /*
         * The mpol_rebind_mm() call takes mmap_sem, which we couldn't
         * take while holding tasklist_lock.  Forks can happen - the
         * mpol_dup() cpuset_being_rebound check will catch such forks,
         * and rebind their vma mempolicies too.  Because we still hold
         * the global cgroup_mutex, we know that no other rebind effort
         * will be contending for the global variable cpuset_being_rebound.
         * It's ok if we rebind the same mm twice; mpol_rebind_mm()
         * is idempotent.  Also migrate pages in each mm to new nodes.
         */
        cgroup_scan_tasks(&scan);

        /* We're done rebinding vmas to this cpuset's new mems_allowed. */
        cpuset_being_rebound = NULL;
}

/*
 * Handle user request to change the 'mems' memory placement
 * of a cpuset.  Needs to validate the request, update the
 * cpusets mems_allowed, and for each task in the cpuset,
 * update mems_allowed and rebind task's mempolicy and any vma
 * mempolicies and if the cpuset is marked 'memory_migrate',
 * migrate the tasks pages to the new memory.
 *
 * Call with cgroup_mutex held.  May take callback_mutex during call.
 * Will take tasklist_lock, scan tasklist for tasks in cpuset cs,
 * lock each such tasks mm->mmap_sem, scan its vma's and rebind
 * their mempolicies to the cpusets new mems_allowed.
 */
static int update_nodemask(struct cpuset *cs, struct cpuset *trialcs,
                           const char *buf)
{
        nodemask_t oldmem;
        int retval;
        struct ptr_heap heap;

        /*
         * top_cpuset.mems_allowed tracks node_stats[N_HIGH_MEMORY];
         * it's read-only
         */
        if (cs == &top_cpuset)
                return -EACCES;

        /*
         * An empty mems_allowed is ok iff there are no tasks in the cpuset.
         * Since nodelist_parse() fails on an empty mask, we special case
         * that parsing.  The validate_change() call ensures that cpusets
         * with tasks have memory.
         */
        if (!*buf) {
                nodes_clear(trialcs->mems_allowed);
        } else {
                retval = nodelist_parse(buf, trialcs->mems_allowed);
                if (retval < 0)
                        goto done;

                if (!nodes_subset(trialcs->mems_allowed,
                                node_states[N_HIGH_MEMORY]))
                        return -EINVAL;
        }
        oldmem = cs->mems_allowed;
        if (nodes_equal(oldmem, trialcs->mems_allowed)) {
                retval = 0;             /* Too easy - nothing to do */
                goto done;
        }
        retval = validate_change(cs, trialcs);
        if (retval < 0)
                goto done;

        retval = heap_init(&heap, PAGE_SIZE, GFP_KERNEL, NULL);
        if (retval < 0)
                goto done;

        mutex_lock(&callback_mutex);
        cs->mems_allowed = trialcs->mems_allowed;
        mutex_unlock(&callback_mutex);

        update_tasks_nodemask(cs, &oldmem, &heap);

        heap_free(&heap);
done:
        return retval;
}

int current_cpuset_is_being_rebound(void)
{
        return task_cs(current) == cpuset_being_rebound;
}

static int update_relax_domain_level(struct cpuset *cs, s64 val)
{
#ifdef CONFIG_SMP
        if (val < -1 || val >= SD_LV_MAX)
                return -EINVAL;
#endif

        if (val != cs->relax_domain_level) {
                cs->relax_domain_level = val;
                if (!cpumask_empty(cs->cpus_allowed) &&
                    is_sched_load_balance(cs))
                        async_rebuild_sched_domains();
        }

        return 0;
}

/*
 * cpuset_change_flag - make a task's spread flags the same as its cpuset's
 * @tsk: task to be updated
 * @scan: struct cgroup_scanner containing the cgroup of the task
 *
 * Called by cgroup_scan_tasks() for each task in a cgroup.
 *
 * We don't need to re-check for the cgroup/cpuset membership, since we're
 * holding cgroup_lock() at this point.
 */
static void cpuset_change_flag(struct task_struct *tsk,
                                struct cgroup_scanner *scan)
{
        cpuset_update_task_spread_flag(cgroup_cs(scan->cg), tsk);
}

/*
 * update_tasks_flags - update the spread flags of tasks in the cpuset.
 * @cs: the cpuset in which each task's spread flags needs to be changed
 * @heap: if NULL, defer allocating heap memory to cgroup_scan_tasks()
 *
 * Called with cgroup_mutex held
 *
 * The cgroup_scan_tasks() function will scan all the tasks in a cgroup,
 * calling callback functions for each.
 *
 * No return value. It's guaranteed that cgroup_scan_tasks() always returns 0
 * if @heap != NULL.
 */
static void update_tasks_flags(struct cpuset *cs, struct ptr_heap *heap)
{
        struct cgroup_scanner scan;

        scan.cg = cs->css.cgroup;
        scan.test_task = NULL;
        scan.process_task = cpuset_change_flag;
        scan.heap = heap;
        cgroup_scan_tasks(&scan);
}

/*
 * update_flag - read a 0 or a 1 in a file and update associated flag
 * bit:         the bit to update (see cpuset_flagbits_t)
 * cs:          the cpuset to update
 * turning_on:  whether the flag is being set or cleared
 *
 * Call with cgroup_mutex held.
 */

static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
                       int turning_on)
{
        struct cpuset *trialcs;
        int balance_flag_changed;
        int spread_flag_changed;
        struct ptr_heap heap;
        int err;

        trialcs = alloc_trial_cpuset(cs);
        if (!trialcs)
                return -ENOMEM;

        if (turning_on)
                set_bit(bit, &trialcs->flags);
        else
                clear_bit(bit, &trialcs->flags);

        err = validate_change(cs, trialcs);
        if (err < 0)
                goto out;

        err = heap_init(&heap, PAGE_SIZE, GFP_KERNEL, NULL);
        if (err < 0)
                goto out;

        balance_flag_changed = (is_sched_load_balance(cs) !=
                                is_sched_load_balance(trialcs));

        spread_flag_changed = ((is_spread_slab(cs) != is_spread_slab(trialcs))
                        || (is_spread_page(cs) != is_spread_page(trialcs)));

        mutex_lock(&callback_mutex);
        cs->flags = trialcs->flags;
        mutex_unlock(&callback_mutex);

        if (!cpumask_empty(trialcs->cpus_allowed) && balance_flag_changed)
                async_rebuild_sched_domains();

        if (spread_flag_changed)
                update_tasks_flags(cs, &heap);
        heap_free(&heap);
out:
        free_trial_cpuset(trialcs);
        return err;
}

/*
 * Frequency meter - How fast is some event occurring?
 *
 * These routines manage a digitally filtered, constant time based,
 * event frequency meter.  There are four routines:
 *   fmeter_init() - initialize a frequency meter.
 *   fmeter_markevent() - called each time the event happens.
 *   fmeter_getrate() - returns the recent rate of such events.
 *   fmeter_update() - internal routine used to update fmeter.
 *
 * A common data structure is passed to each of these routines,
 * which is used to keep track of the state required to manage the
 * frequency meter and its digital filter.
 *
 * The filter works on the number of events marked per unit time.
 * The filter is single-pole low-pass recursive (IIR).  The time unit
 * is 1 second.  Arithmetic is done using 32-bit integers scaled to
 * simulate 3 decimal digits of precision (multiplied by 1000).
 *
 * With an FM_COEF of 933, and a time base of 1 second, the filter
 * has a half-life of 10 seconds, meaning that if the events quit
 * happening, then the rate returned from the fmeter_getrate()
 * will be cut in half each 10 seconds, until it converges to zero.
 *
 * It is not worth doing a real infinitely recursive filter.  If more
 * than FM_MAXTICKS ticks have elapsed since the last filter event,
 * just compute FM_MAXTICKS ticks worth, by which point the level
 * will be stable.
 *
 * Limit the count of unprocessed events to FM_MAXCNT, so as to avoid
 * arithmetic overflow in the fmeter_update() routine.
 *
 * Given the simple 32 bit integer arithmetic used, this meter works
 * best for reporting rates between one per millisecond (msec) and
 * one per 32 (approx) seconds.  At constant rates faster than one
 * per msec it maxes out at values just under 1,000,000.  At constant
 * rates between one per msec, and one per second it will stabilize
 * to a value N*1000, where N is the rate of events per second.
 * At constant rates between one per second and one per 32 seconds,
 * it will be choppy, moving up on the seconds that have an event,
 * and then decaying until the next event.  At rates slower than
 * about one in 32 seconds, it decays all the way back to zero between
 * each event.
 */

#define FM_COEF 933             /* coefficient for half-life of 10 secs */
#define FM_MAXTICKS ((time_t)99) /* useless computing more ticks than this */
#define FM_MAXCNT 1000000       /* limit cnt to avoid overflow */
#define FM_SCALE 1000           /* faux fixed point scale */

/* Initialize a frequency meter */
static void fmeter_init(struct fmeter *fmp)
{
        fmp->cnt = 0;
        fmp->val = 0;
        fmp->time = 0;
        spin_lock_init(&fmp->lock);
}

/* Internal meter update - process cnt events and update value */
static void fmeter_update(struct fmeter *fmp)
{
        time_t now = get_seconds();
        time_t ticks = now - fmp->time;

        if (ticks == 0)
                return;

        ticks = min(FM_MAXTICKS, ticks);
        while (ticks-- > 0)
                fmp->val = (FM_COEF * fmp->val) / FM_SCALE;
        fmp->time = now;

        fmp->val += ((FM_SCALE - FM_COEF) * fmp->cnt) / FM_SCALE;
        fmp->cnt = 0;
}

/* Process any previous ticks, then bump cnt by one (times scale). */
static void fmeter_markevent(struct fmeter *fmp)
{
        spin_lock(&fmp->lock);
        fmeter_update(fmp);
        fmp->cnt = min(FM_MAXCNT, fmp->cnt + FM_SCALE);
        spin_unlock(&fmp->lock);
}

/* Process any previous ticks, then return current value. */
static int fmeter_getrate(struct fmeter *fmp)
{
        int val;

        spin_lock(&fmp->lock);
        fmeter_update(fmp);
        val = fmp->val;
        spin_unlock(&fmp->lock);
        return val;
}

/* Protected by cgroup_lock */
static cpumask_var_t cpus_attach;

/* Called by cgroups to determine if a cpuset is usable; cgroup_mutex held */
static int cpuset_can_attach(struct cgroup_subsys *ss, struct cgroup *cont,
                             struct task_struct *tsk, bool threadgroup)
{
        int ret;
        struct cpuset *cs = cgroup_cs(cont);

        if (cpumask_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed))
                return -ENOSPC;

        /*
         * Kthreads bound to specific cpus cannot be moved to a new cpuset; we
         * cannot change their cpu affinity and isolating such threads by their
         * set of allowed nodes is unnecessary.  Thus, cpusets are not
         * applicable for such threads.  This prevents checking for success of
         * set_cpus_allowed_ptr() on all attached tasks before cpus_allowed may
         * be changed.
         */
        if (tsk->flags & PF_THREAD_BOUND)
                return -EINVAL;

        ret = security_task_setscheduler(tsk, 0, NULL);
        if (ret)
                return ret;
        if (threadgroup) {
                struct task_struct *c;

                rcu_read_lock();
                list_for_each_entry_rcu(c, &tsk->thread_group, thread_group) {
                        ret = security_task_setscheduler(c, 0, NULL);
                        if (ret) {
                                rcu_read_unlock();
                                return ret;
                        }
                }
                rcu_read_unlock();
        }
        return 0;
}

static void cpuset_attach_task(struct task_struct *tsk, nodemask_t *to,
                               struct cpuset *cs)
{
        int err;
        /*
         * can_attach beforehand should guarantee that this doesn't fail.
         * TODO: have a better way to handle failure here
         */
        err = set_cpus_allowed_ptr(tsk, cpus_attach);
        WARN_ON_ONCE(err);

        task_lock(tsk);
        cpuset_change_task_nodemask(tsk, to);
        task_unlock(tsk);
        cpuset_update_task_spread_flag(cs, tsk);

}

static void cpuset_attach(struct cgroup_subsys *ss, struct cgroup *cont,
                          struct cgroup *oldcont, struct task_struct *tsk,
                          bool threadgroup)
{
        nodemask_t from, to;
        struct mm_struct *mm;
        struct cpuset *cs = cgroup_cs(cont);
        struct cpuset *oldcs = cgroup_cs(oldcont);

        if (cs == &top_cpuset) {
                cpumask_copy(cpus_attach, cpu_possible_mask);
        } else {
                guarantee_online_cpus(cs, cpus_attach);
        }
        guarantee_online_mems(cs, &to);

        /* do per-task migration stuff possibly for each in the threadgroup */
        cpuset_attach_task(tsk, &to, cs);
        if (threadgroup) {
                struct task_struct *c;
                rcu_read_lock();
                list_for_each_entry_rcu(c, &tsk->thread_group, thread_group) {
                        cpuset_attach_task(c, &to, cs);
                }
                rcu_read_unlock();
        }

        /* change mm; only needs to be done once even if threadgroup */
        from = oldcs->mems_allowed;
        to = cs->mems_allowed;
        mm = get_task_mm(tsk);
        if (mm) {
                mpol_rebind_mm(mm, &to);
                if (is_memory_migrate(cs))
                        cpuset_migrate_mm(mm, &from, &to);
                mmput(mm);
        }
}

/* The various types of files and directories in a cpuset file system */

typedef enum {
        FILE_MEMORY_MIGRATE,
        FILE_CPULIST,
        FILE_MEMLIST,
        FILE_CPU_EXCLUSIVE,
        FILE_MEM_EXCLUSIVE,
        FILE_MEM_HARDWALL,
        FILE_SCHED_LOAD_BALANCE,
        FILE_SCHED_RELAX_DOMAIN_LEVEL,
        FILE_MEMORY_PRESSURE_ENABLED,
        FILE_MEMORY_PRESSURE,
        FILE_SPREAD_PAGE,
        FILE_SPREAD_SLAB,
} cpuset_filetype_t;

static int cpuset_write_u64(struct cgroup *cgrp, struct cftype *cft, u64 val)
{
        int retval = 0;
        struct cpuset *cs = cgroup_cs(cgrp);
        cpuset_filetype_t type = cft->private;

        if (!cgroup_lock_live_group(cgrp))
                return -ENODEV;

        switch (type) {
        case FILE_CPU_EXCLUSIVE:
                retval = update_flag(CS_CPU_EXCLUSIVE, cs, val);
                break;
        case FILE_MEM_EXCLUSIVE:
                retval = update_flag(CS_MEM_EXCLUSIVE, cs, val);
                break;
        case FILE_MEM_HARDWALL:
                retval = update_flag(CS_MEM_HARDWALL, cs, val);
                break;
        case FILE_SCHED_LOAD_BALANCE:
                retval = update_flag(CS_SCHED_LOAD_BALANCE, cs, val);
                break;
        case FILE_MEMORY_MIGRATE:
                retval = update_flag(CS_MEMORY_MIGRATE, cs, val);
                break;
        case FILE_MEMORY_PRESSURE_ENABLED:
                cpuset_memory_pressure_enabled = !!val;
                break;
        case FILE_MEMORY_PRESSURE:
                retval = -EACCES;
                break;
        case FILE_SPREAD_PAGE:
                retval = update_flag(CS_SPREAD_PAGE, cs, val);
                break;
        case FILE_SPREAD_SLAB:
                retval = update_flag(CS_SPREAD_SLAB, cs, val);
                break;
        default:
                retval = -EINVAL;
                break;
        }
        cgroup_unlock();
        return retval;
}

static int cpuset_write_s64(struct cgroup *cgrp, struct cftype *cft, s64 val)
{
        int retval = 0;
        struct cpuset *cs = cgroup_cs(cgrp);
        cpuset_filetype_t type = cft->private;

        if (!cgroup_lock_live_group(cgrp))
                return -ENODEV;

        switch (type) {
        case FILE_SCHED_RELAX_DOMAIN_LEVEL:
                retval = update_relax_domain_level(cs, val);
                break;
        default:
                retval = -EINVAL;
                break;
        }
        cgroup_unlock();
        return retval;
}

/*
 * Common handling for a write to a "cpus" or "mems" file.
 */
static int cpuset_write_resmask(struct cgroup *cgrp, struct cftype *cft,
                                const char *buf)
{
        int retval = 0;
        struct cpuset *cs = cgroup_cs(cgrp);
        struct cpuset *trialcs;

        if (!cgroup_lock_live_group(cgrp))
                return -ENODEV;

        trialcs = alloc_trial_cpuset(cs);
        if (!trialcs) {
                retval = -ENOMEM;
                goto out;
        }

        switch (cft->private) {
        case FILE_CPULIST:
                retval = update_cpumask(cs, trialcs, buf);
                break;
        case FILE_MEMLIST:
                retval = update_nodemask(cs, trialcs, buf);
                break;
        default:
                retval = -EINVAL;
                break;
        }

        free_trial_cpuset(trialcs);
out:
        cgroup_unlock();
        return retval;
}

/*
 * These ascii lists should be read in a single call, by using a user
 * buffer large enough to hold the entire map.  If read in smaller
 * chunks, there is no guarantee of atomicity.  Since the display format
 * used, list of ranges of sequential numbers, is variable length,
 * and since these maps can change value dynamically, one could read
 * gibberish by doing partial reads while a list was changing.
 * A single large read to a buffer that crosses a page boundary is
 * ok, because the result being copied to user land is not recomputed
 * across a page fault.
 */

static int cpuset_sprintf_cpulist(char *page, struct cpuset *cs)
{
        int ret;

        mutex_lock(&callback_mutex);
        ret = cpulist_scnprintf(page, PAGE_SIZE, cs->cpus_allowed);
        mutex_unlock(&callback_mutex);

        return ret;
}

static int cpuset_sprintf_memlist(char *page, struct cpuset *cs)
{
        nodemask_t mask;

        mutex_lock(&callback_mutex);
        mask = cs->mems_allowed;
        mutex_unlock(&callback_mutex);

        return nodelist_scnprintf(page, PAGE_SIZE, mask);
}

static ssize_t cpuset_common_file_read(struct cgroup *cont,
                                       struct cftype *cft,
                                       struct file *file,
                                       char __user *buf,
                                       size_t nbytes, loff_t *ppos)
{
        struct cpuset *cs = cgroup_cs(cont);
        cpuset_filetype_t type = cft->private;
        char *page;
        ssize_t retval = 0;
        char *s;

        if (!(page = (char *)__get_free_page(GFP_TEMPORARY)))
                return -ENOMEM;

        s = page;

        switch (type) {
        case FILE_CPULIST:
                s += cpuset_sprintf_cpulist(s, cs);
                break;
        case FILE_MEMLIST:
                s += cpuset_sprintf_memlist(s, cs);
                break;
        default:
                retval = -EINVAL;
                goto out;
        }
        *s++ = '\n';

        retval = simple_read_from_buffer(buf, nbytes, ppos, page, s - page);
out:
        free_page((unsigned long)page);
        return retval;
}

static u64 cpuset_read_u64(struct cgroup *cont, struct cftype *cft)
{
        struct cpuset *cs = cgroup_cs(cont);
        cpuset_filetype_t type = cft->private;
        switch (type) {
        case FILE_CPU_EXCLUSIVE:
                return is_cpu_exclusive(cs);
        case FILE_MEM_EXCLUSIVE:
                return is_mem_exclusive(cs);
        case FILE_MEM_HARDWALL:
                return is_mem_hardwall(cs);
        case FILE_SCHED_LOAD_BALANCE:
                return is_sched_load_balance(cs);
        case FILE_MEMORY_MIGRATE:
                return is_memory_migrate(cs);
        case FILE_MEMORY_PRESSURE_ENABLED:
                return cpuset_memory_pressure_enabled;
        case FILE_MEMORY_PRESSURE:
                return fmeter_getrate(&cs->fmeter);
        case FILE_SPREAD_PAGE:
                return is_spread_page(cs);
        case FILE_SPREAD_SLAB:
                return is_spread_slab(cs);
        default:
                BUG();
        }

        /* Unreachable but makes gcc happy */
        return 0;
}

static s64 cpuset_read_s64(struct cgroup *cont, struct cftype *cft)
{
        struct cpuset *cs = cgroup_cs(cont);
        cpuset_filetype_t type = cft->private;
        switch (type) {
        case FILE_SCHED_RELAX_DOMAIN_LEVEL:
                return cs->relax_domain_level;
        default:
                BUG();
        }

        /* Unrechable but makes gcc happy */
        return 0;
}


/*
 * for the common functions, 'private' gives the type of file
 */

static struct cftype files[] = {
        {
                .name = "cpus",
                .read = cpuset_common_file_read,
                .write_string = cpuset_write_resmask,
                .max_write_len = (100U + 6 * NR_CPUS),
                .private = FILE_CPULIST,
        },

        {
                .name = "mems",
                .read = cpuset_common_file_read,
                .write_string = cpuset_write_resmask,
                .max_write_len = (100U + 6 * MAX_NUMNODES),
                .private = FILE_MEMLIST,
        },

        {
                .name = "cpu_exclusive",
                .read_u64 = cpuset_read_u64,
                .write_u64 = cpuset_write_u64,
                .private = FILE_CPU_EXCLUSIVE,
        },

        {
                .name = "mem_exclusive",
                .read_u64 = cpuset_read_u64,
                .write_u64 = cpuset_write_u64,
                .private = FILE_MEM_EXCLUSIVE,
        },

        {
                .name = "mem_hardwall",
                .read_u64 = cpuset_read_u64,
                .write_u64 = cpuset_write_u64,
                .private = FILE_MEM_HARDWALL,
        },

        {
                .name = "sched_load_balance",
                .read_u64 = cpuset_read_u64,
                .write_u64 = cpuset_write_u64,
                .private = FILE_SCHED_LOAD_BALANCE,
        },

        {
                .name = "sched_relax_domain_level",
                .read_s64 = cpuset_read_s64,
                .write_s64 = cpuset_write_s64,
                .private = FILE_SCHED_RELAX_DOMAIN_LEVEL,
        },

        {
                .name = "memory_migrate",
                .read_u64 = cpuset_read_u64,
                .write_u64 = cpuset_write_u64,
                .private = FILE_MEMORY_MIGRATE,
        },

        {
                .name = "memory_pressure",
                .read_u64 = cpuset_read_u64,
                .write_u64 = cpuset_write_u64,
                .private = FILE_MEMORY_PRESSURE,
                .mode = S_IRUGO,
        },

        {
                .name = "memory_spread_page",
                .read_u64 = cpuset_read_u64,
                .write_u64 = cpuset_write_u64,
                .private = FILE_SPREAD_PAGE,
        },

        {
                .name = "memory_spread_slab",
                .read_u64 = cpuset_read_u64,
                .write_u64 = cpuset_write_u64,
                .private = FILE_SPREAD_SLAB,
        },
};

static struct cftype cft_memory_pressure_enabled = {
        .name = "memory_pressure_enabled",
        .read_u64 = cpuset_read_u64,
        .write_u64 = cpuset_write_u64,
        .private = FILE_MEMORY_PRESSURE_ENABLED,
};

static int cpuset_populate(struct cgroup_subsys *ss, struct cgroup *cont)
{
        int err;

        err = cgroup_add_files(cont, ss, files, ARRAY_SIZE(files));
        if (err)
                return err;
        /* memory_pressure_enabled is in root cpuset only */
        if (!cont->parent)
                err = cgroup_add_file(cont, ss,
                                      &cft_memory_pressure_enabled);
        return err;
}

/*
 * post_clone() is called at the end of cgroup_clone().
 * 'cgroup' was just created automatically as a result of
 * a cgroup_clone(), and the current task is about to
 * be moved into 'cgroup'.
 *
 * Currently we refuse to set up the cgroup - thereby
 * refusing the task to be entered, and as a result refusing
 * the sys_unshare() or clone() which initiated it - if any
 * sibling cpusets have exclusive cpus or mem.
 *
 * If this becomes a problem for some users who wish to
 * allow that scenario, then cpuset_post_clone() could be
 * changed to grant parent->cpus_allowed-sibling_cpus_exclusive
 * (and likewise for mems) to the new cgroup. Called with cgroup_mutex
 * held.
 */
static void cpuset_post_clone(struct cgroup_subsys *ss,
                              struct cgroup *cgroup)
{
        struct cgroup *parent, *child;
        struct cpuset *cs, *parent_cs;

        parent = cgroup->parent;
        list_for_each_entry(child, &parent->children, sibling) {
                cs = cgroup_cs(child);
                if (is_mem_exclusive(cs) || is_cpu_exclusive(cs))
                        return;
        }
        cs = cgroup_cs(cgroup);
        parent_cs = cgroup_cs(parent);

        cs->mems_allowed = parent_cs->mems_allowed;
        cpumask_copy(cs->cpus_allowed, parent_cs->cpus_allowed);
        return;
}

/*
 *      cpuset_create - create a cpuset
 *      ss:     cpuset cgroup subsystem
 *      cont:   control group that the new cpuset will be part of
 */

static struct cgroup_subsys_state *cpuset_create(
        struct cgroup_subsys *ss,
        struct cgroup *cont)
{
        struct cpuset *cs;
        struct cpuset *parent;

        if (!cont->parent) {
                return &top_cpuset.css;
        }
        parent = cgroup_cs(cont->parent);
        cs = kmalloc(sizeof(*cs), GFP_KERNEL);
        if (!cs)
                return ERR_PTR(-ENOMEM);
        if (!alloc_cpumask_var(&cs->cpus_allowed, GFP_KERNEL)) {
                kfree(cs);
                return ERR_PTR(-ENOMEM);
        }

        cs->flags = 0;
        if (is_spread_page(parent))
                set_bit(CS_SPREAD_PAGE, &cs->flags);
        if (is_spread_slab(parent))
                set_bit(CS_SPREAD_SLAB, &cs->flags);
        set_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
        cpumask_clear(cs->cpus_allowed);
        nodes_clear(cs->mems_allowed);
        fmeter_init(&cs->fmeter);
        cs->relax_domain_level = -1;

        cs->parent = parent;
        number_of_cpusets++;
        return &cs->css ;
}

/*
 * If the cpuset being removed has its flag 'sched_load_balance'
 * enabled, then simulate turning sched_load_balance off, which
 * will call async_rebuild_sched_domains().
 */

static void cpuset_destroy(struct cgroup_subsys *ss, struct cgroup *cont)
{
        struct cpuset *cs = cgroup_cs(cont);

        if (is_sched_load_balance(cs))
                update_flag(CS_SCHED_LOAD_BALANCE, cs, 0);

        number_of_cpusets--;
        free_cpumask_var(cs->cpus_allowed);
        kfree(cs);
}

struct cgroup_subsys cpuset_subsys = {
        .name = "cpuset",
        .create = cpuset_create,
        .destroy = cpuset_destroy,
        .can_attach = cpuset_can_attach,
        .attach = cpuset_attach,
        .populate = cpuset_populate,
        .post_clone = cpuset_post_clone,
        .subsys_id = cpuset_subsys_id,
        .early_init = 1,
};

/**
 * cpuset_init - initialize cpusets at system boot
 *
 * Description: Initialize top_cpuset and the cpuset internal file system,
 **/

int __init cpuset_init(void)
{
        int err = 0;

        if (!alloc_cpumask_var(&top_cpuset.cpus_allowed, GFP_KERNEL))
                BUG();

        cpumask_setall(top_cpuset.cpus_allowed);
        nodes_setall(top_cpuset.mems_allowed);

        fmeter_init(&top_cpuset.fmeter);
        set_bit(CS_SCHED_LOAD_BALANCE, &top_cpuset.flags);
        top_cpuset.relax_domain_level = -1;

        err = register_filesystem(&cpuset_fs_type);
        if (err < 0)
                return err;

        if (!alloc_cpumask_var(&cpus_attach, GFP_KERNEL))
                BUG();

        number_of_cpusets = 1;
        return 0;
}

/**
 * cpuset_do_move_task - move a given task to another cpuset
 * @tsk: pointer to task_struct the task to move
 * @scan: struct cgroup_scanner contained in its struct cpuset_hotplug_scanner
 *
 * Called by cgroup_scan_tasks() for each task in a cgroup.
 * Return nonzero to stop the walk through the tasks.
 */
static void cpuset_do_move_task(struct task_struct *tsk,
                                struct cgroup_scanner *scan)
{
        struct cgroup *new_cgroup = scan->data;

        cgroup_attach_task(new_cgroup, tsk);
}

/**
 * move_member_tasks_to_cpuset - move tasks from one cpuset to another
 * @from: cpuset in which the tasks currently reside
 * @to: cpuset to which the tasks will be moved
 *
 * Called with cgroup_mutex held
 * callback_mutex must not be held, as cpuset_attach() will take it.
 *
 * The cgroup_scan_tasks() function will scan all the tasks in a cgroup,
 * calling callback functions for each.
 */
static void move_member_tasks_to_cpuset(struct cpuset *from, struct cpuset *to)
{
        struct cgroup_scanner scan;

        scan.cg = from->css.cgroup;
        scan.test_task = NULL; /* select all tasks in cgroup */
        scan.process_task = cpuset_do_move_task;
        scan.heap = NULL;
        scan.data = to->css.cgroup;

        if (cgroup_scan_tasks(&scan))
                printk(KERN_ERR "move_member_tasks_to_cpuset: "
                                "cgroup_scan_tasks failed\n");
}

/*
 * If CPU and/or memory hotplug handlers, below, unplug any CPUs
 * or memory nodes, we need to walk over the cpuset hierarchy,
 * removing that CPU or node from all cpusets.  If this removes the
 * last CPU or node from a cpuset, then move the tasks in the empty
 * cpuset to its next-highest non-empty parent.
 *
 * Called with cgroup_mutex held
 * callback_mutex must not be held, as cpuset_attach() will take it.
 */
static void remove_tasks_in_empty_cpuset(struct cpuset *cs)
{
        struct cpuset *parent;

        /*
         * The cgroup's css_sets list is in use if there are tasks
         * in the cpuset; the list is empty if there are none;
         * the cs->css.refcnt seems always 0.
         */
        if (list_empty(&cs->css.cgroup->css_sets))
                return;

        /*
         * Find its next-highest non-empty parent, (top cpuset
         * has online cpus, so can't be empty).
         */
        parent = cs->parent;
        while (cpumask_empty(parent->cpus_allowed) ||
                        nodes_empty(parent->mems_allowed))
                parent = parent->parent;

        move_member_tasks_to_cpuset(cs, parent);
}

/*
 * Walk the specified cpuset subtree and look for empty cpusets.
 * The tasks of such cpuset must be moved to a parent cpuset.
 *
 * Called with cgroup_mutex held.  We take callback_mutex to modify
 * cpus_allowed and mems_allowed.
 *
 * This walk processes the tree from top to bottom, completing one layer
 * before dropping down to the next.  It always processes a node before
 * any of its children.
 *
 * For now, since we lack memory hot unplug, we'll never see a cpuset
 * that has tasks along with an empty 'mems'.  But if we did see such
 * a cpuset, we'd handle it just like we do if its 'cpus' was empty.
 */
static void scan_for_empty_cpusets(struct cpuset *root)
{
        LIST_HEAD(queue);
        struct cpuset *cp;      /* scans cpusets being updated */
        struct cpuset *child;   /* scans child cpusets of cp */
        struct cgroup *cont;
        nodemask_t oldmems;

        list_add_tail((struct list_head *)&root->stack_list, &queue);

        while (!list_empty(&queue)) {
                cp = list_first_entry(&queue, struct cpuset, stack_list);
                list_del(queue.next);
                list_for_each_entry(cont, &cp->css.cgroup->children, sibling) {
                        child = cgroup_cs(cont);
                        list_add_tail(&child->stack_list, &queue);
                }

                /* Continue past cpusets with all cpus, mems online */
                if (cpumask_subset(cp->cpus_allowed, cpu_active_mask) &&
                    nodes_subset(cp->mems_allowed, node_states[N_HIGH_MEMORY]))
                        continue;

                oldmems = cp->mems_allowed;

                /* Remove offline cpus and mems from this cpuset. */
                mutex_lock(&callback_mutex);
                cpumask_and(cp->cpus_allowed, cp->cpus_allowed,
                            cpu_active_mask);
                nodes_and(cp->mems_allowed, cp->mems_allowed,
                                                node_states[N_HIGH_MEMORY]);
                mutex_unlock(&callback_mutex);

                /* Move tasks from the empty cpuset to a parent */
                if (cpumask_empty(cp->cpus_allowed) ||
                     nodes_empty(cp->mems_allowed))
                        remove_tasks_in_empty_cpuset(cp);
                else {
                        update_tasks_cpumask(cp, NULL);
                        update_tasks_nodemask(cp, &oldmems, NULL);
                }
        }
}

/*
 * The top_cpuset tracks what CPUs and Memory Nodes are online,
 * period.  This is necessary in order to make cpusets transparent
 * (of no affect) on systems that are actively using CPU hotplug
 * but making no active use of cpusets.
 *
 * This routine ensures that top_cpuset.cpus_allowed tracks
 * cpu_online_map on each CPU hotplug (cpuhp) event.
 *
 * Called within get_online_cpus().  Needs to call cgroup_lock()
 * before calling generate_sched_domains().
 */
static int cpuset_track_online_cpus(struct notifier_block *unused_nb,
                                unsigned long phase, void *unused_cpu)
{
        struct sched_domain_attr *attr;
        cpumask_var_t *doms;
        int ndoms;

        switch (phase) {
        case CPU_ONLINE:
        case CPU_ONLINE_FROZEN:
        case CPU_DOWN_PREPARE:
        case CPU_DOWN_PREPARE_FROZEN:
        case CPU_DOWN_FAILED:
        case CPU_DOWN_FAILED_FROZEN:
                break;

        default:
                return NOTIFY_DONE;
        }

        cgroup_lock();
        mutex_lock(&callback_mutex);
        cpumask_copy(top_cpuset.cpus_allowed, cpu_active_mask);
        mutex_unlock(&callback_mutex);
        scan_for_empty_cpusets(&top_cpuset);
        ndoms = generate_sched_domains(&doms, &attr);
        cgroup_unlock();

        /* Have scheduler rebuild the domains */
        partition_sched_domains(ndoms, doms, attr);

        return NOTIFY_OK;
}

#ifdef CONFIG_MEMORY_HOTPLUG
/*
 * Keep top_cpuset.mems_allowed tracking node_states[N_HIGH_MEMORY].
 * Call this routine anytime after node_states[N_HIGH_MEMORY] changes.
 * See also the previous routine cpuset_track_online_cpus().
 */
static int cpuset_track_online_nodes(struct notifier_block *self,
                                unsigned long action, void *arg)
{
        nodemask_t oldmems;

        cgroup_lock();
        switch (action) {
        case MEM_ONLINE:
                oldmems = top_cpuset.mems_allowed;
                mutex_lock(&callback_mutex);
                top_cpuset.mems_allowed = node_states[N_HIGH_MEMORY];
                mutex_unlock(&callback_mutex);
                update_tasks_nodemask(&top_cpuset, &oldmems, NULL);
                break;
        case MEM_OFFLINE:
                /*
                 * needn't update top_cpuset.mems_allowed explicitly because
                 * scan_for_empty_cpusets() will update it.
                 */
                scan_for_empty_cpusets(&top_cpuset);
                break;
        default:
                break;
        }
        cgroup_unlock();
        return NOTIFY_OK;
}
#endif

/**
 * cpuset_init_smp - initialize cpus_allowed
 *
 * Description: Finish top cpuset after cpu, node maps are initialized
 **/

void __init cpuset_init_smp(void)
{
        cpumask_copy(top_cpuset.cpus_allowed, cpu_active_mask);
        top_cpuset.mems_allowed = node_states[N_HIGH_MEMORY];

        hotcpu_notifier(cpuset_track_online_cpus, 0);
        hotplug_memory_notifier(cpuset_track_online_nodes, 10);

        cpuset_wq = create_singlethread_workqueue("cpuset");
        BUG_ON(!cpuset_wq);
}

/**
 * cpuset_cpus_allowed - return cpus_allowed mask from a tasks cpuset.
 * @tsk: pointer to task_struct from which to obtain cpuset->cpus_allowed.
 * @pmask: pointer to struct cpumask variable to receive cpus_allowed set.
 *
 * Description: Returns the cpumask_var_t cpus_allowed of the cpuset
 * attached to the specified @tsk.  Guaranteed to return some non-empty
 * subset of cpu_online_map, even if this means going outside the
 * tasks cpuset.
 **/

void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
{
        mutex_lock(&callback_mutex);
        cpuset_cpus_allowed_locked(tsk, pmask);
        mutex_unlock(&callback_mutex);
}

/**
 * cpuset_cpus_allowed_locked - return cpus_allowed mask from a tasks cpuset.
 * Must be called with callback_mutex held.
 **/
void cpuset_cpus_allowed_locked(struct task_struct *tsk, struct cpumask *pmask)
{
        task_lock(tsk);
        guarantee_online_cpus(task_cs(tsk), pmask);
        task_unlock(tsk);
}

void cpuset_init_current_mems_allowed(void)
{
        nodes_setall(current->mems_allowed);
}

/**
 * cpuset_mems_allowed - return mems_allowed mask from a tasks cpuset.
 * @tsk: pointer to task_struct from which to obtain cpuset->mems_allowed.
 *
 * Description: Returns the nodemask_t mems_allowed of the cpuset
 * attached to the specified @tsk.  Guaranteed to return some non-empty
 * subset of node_states[N_HIGH_MEMORY], even if this means going outside the
 * tasks cpuset.
 **/

nodemask_t cpuset_mems_allowed(struct task_struct *tsk)
{
        nodemask_t mask;

        mutex_lock(&callback_mutex);
        task_lock(tsk);
        guarantee_online_mems(task_cs(tsk), &mask);
        task_unlock(tsk);
        mutex_unlock(&callback_mutex);

        return mask;
}

/**
 * cpuset_nodemask_valid_mems_allowed - check nodemask vs. curremt mems_allowed
 * @nodemask: the nodemask to be checked
 *
 * Are any of the nodes in the nodemask allowed in current->mems_allowed?
 */
int cpuset_nodemask_valid_mems_allowed(nodemask_t *nodemask)
{
        return nodes_intersects(*nodemask, current->mems_allowed);
}

/*
 * nearest_hardwall_ancestor() - Returns the nearest mem_exclusive or
 * mem_hardwall ancestor to the specified cpuset.  Call holding
 * callback_mutex.  If no ancestor is mem_exclusive or mem_hardwall
 * (an unusual configuration), then returns the root cpuset.
 */
static const struct cpuset *nearest_hardwall_ancestor(const struct cpuset *cs)
{
        while (!(is_mem_exclusive(cs) || is_mem_hardwall(cs)) && cs->parent)
                cs = cs->parent;
        return cs;
}

/**
 * cpuset_node_allowed_softwall - Can we allocate on a memory node?
 * @node: is this an allowed node?
 * @gfp_mask: memory allocation flags
 *
 * If we're in interrupt, yes, we can always allocate.  If __GFP_THISNODE is
 * set, yes, we can always allocate.  If node is in our task's mems_allowed,
 * yes.  If it's not a __GFP_HARDWALL request and this node is in the nearest
 * hardwalled cpuset ancestor to this task's cpuset, yes.  If the task has been
 * OOM killed and has access to memory reserves as specified by the TIF_MEMDIE
 * flag, yes.
 * Otherwise, no.
 *
 * If __GFP_HARDWALL is set, cpuset_node_allowed_softwall() reduces to
 * cpuset_node_allowed_hardwall().  Otherwise, cpuset_node_allowed_softwall()
 * might sleep, and might allow a node from an enclosing cpuset.
 *
 * cpuset_node_allowed_hardwall() only handles the simpler case of hardwall
 * cpusets, and never sleeps.
 *
 * The __GFP_THISNODE placement logic is really handled elsewhere,
 * by forcibly using a zonelist starting at a specified node, and by
 * (in get_page_from_freelist()) refusing to consider the zones for
 * any node on the zonelist except the first.  By the time any such
 * calls get to this routine, we should just shut up and say 'yes'.
 *
 * GFP_USER allocations are marked with the __GFP_HARDWALL bit,
 * and do not allow allocations outside the current tasks cpuset
 * unless the task has been OOM killed as is marked TIF_MEMDIE.
 * GFP_KERNEL allocations are not so marked, so can escape to the
 * nearest enclosing hardwalled ancestor cpuset.
 *
 * Scanning up parent cpusets requires callback_mutex.  The
 * __alloc_pages() routine only calls here with __GFP_HARDWALL bit
 * _not_ set if it's a GFP_KERNEL allocation, and all nodes in the
 * current tasks mems_allowed came up empty on the first pass over
 * the zonelist.  So only GFP_KERNEL allocations, if all nodes in the
 * cpuset are short of memory, might require taking the callback_mutex
 * mutex.
 *
 * The first call here from mm/page_alloc:get_page_from_freelist()
 * has __GFP_HARDWALL set in gfp_mask, enforcing hardwall cpusets,
 * so no allocation on a node outside the cpuset is allowed (unless
 * in interrupt, of course).
 *
 * The second pass through get_page_from_freelist() doesn't even call
 * here for GFP_ATOMIC calls.  For those calls, the __alloc_pages()
 * variable 'wait' is not set, and the bit ALLOC_CPUSET is not set
 * in alloc_flags.  That logic and the checks below have the combined
 * affect that:
 *      in_interrupt - any node ok (current task context irrelevant)
 *      GFP_ATOMIC   - any node ok
 *      TIF_MEMDIE   - any node ok
 *      GFP_KERNEL   - any node in enclosing hardwalled cpuset ok
 *      GFP_USER     - only nodes in current tasks mems allowed ok.
 *
 * Rule:
 *    Don't call cpuset_node_allowed_softwall if you can't sleep, unless you
 *    pass in the __GFP_HARDWALL flag set in gfp_flag, which disables
 *    the code that might scan up ancestor cpusets and sleep.
 */
int __cpuset_node_allowed_softwall(int node, gfp_t gfp_mask)
{
        const struct cpuset *cs;        /* current cpuset ancestors */
        int allowed;                    /* is allocation in zone z allowed? */

        if (in_interrupt() || (gfp_mask & __GFP_THISNODE))
                return 1;
        might_sleep_if(!(gfp_mask & __GFP_HARDWALL));
        if (node_isset(node, current->mems_allowed))
                return 1;
        /*
         * Allow tasks that have access to memory reserves because they have
         * been OOM killed to get memory anywhere.
         */
        if (unlikely(test_thread_flag(TIF_MEMDIE)))
                return 1;
        if (gfp_mask & __GFP_HARDWALL)  /* If hardwall request, stop here */
                return 0;

        if (current->flags & PF_EXITING) /* Let dying task have memory */
                return 1;

        /* Not hardwall and node outside mems_allowed: scan up cpusets */
        mutex_lock(&callback_mutex);

        task_lock(current);
        cs = nearest_hardwall_ancestor(task_cs(current));
        task_unlock(current);

        allowed = node_isset(node, cs->mems_allowed);
        mutex_unlock(&callback_mutex);
        return allowed;
}

/*
 * cpuset_node_allowed_hardwall - Can we allocate on a memory node?
 * @node: is this an allowed node?
 * @gfp_mask: memory allocation flags
 *
 * If we're in interrupt, yes, we can always allocate.  If __GFP_THISNODE is
 * set, yes, we can always allocate.  If node is in our task's mems_allowed,
 * yes.  If the task has been OOM killed and has access to memory reserves as
 * specified by the TIF_MEMDIE flag, yes.
 * Otherwise, no.
 *
 * The __GFP_THISNODE placement logic is really handled elsewhere,
 * by forcibly using a zonelist starting at a specified node, and by
 * (in get_page_from_freelist()) refusing to consider the zones for
 * any node on the zonelist except the first.  By the time any such
 * calls get to this routine, we should just shut up and say 'yes'.
 *
 * Unlike the cpuset_node_allowed_softwall() variant, above,
 * this variant requires that the node be in the current task's
 * mems_allowed or that we're in interrupt.  It does not scan up the
 * cpuset hierarchy for the nearest enclosing mem_exclusive cpuset.
 * It never sleeps.
 */
int __cpuset_node_allowed_hardwall(int node, gfp_t gfp_mask)
{
        if (in_interrupt() || (gfp_mask & __GFP_THISNODE))
                return 1;
        if (node_isset(node, current->mems_allowed))
                return 1;
        /*
         * Allow tasks that have access to memory reserves because they have
         * been OOM killed to get memory anywhere.
         */
        if (unlikely(test_thread_flag(TIF_MEMDIE)))
                return 1;
        return 0;
}

/**
 * cpuset_lock - lock out any changes to cpuset structures
 *
 * The out of memory (oom) code needs to mutex_lock cpusets
 * from being changed while it scans the tasklist looking for a
 * task in an overlapping cpuset.  Expose callback_mutex via this
 * cpuset_lock() routine, so the oom code can lock it, before
 * locking the task list.  The tasklist_lock is a spinlock, so
 * must be taken inside callback_mutex.
 */

void cpuset_lock(void)
{
        mutex_lock(&callback_mutex);
}

/**
 * cpuset_unlock - release lock on cpuset changes
 *
 * Undo the lock taken in a previous cpuset_lock() call.
 */

void cpuset_unlock(void)
{
        mutex_unlock(&callback_mutex);
}

/**
 * cpuset_mem_spread_node() - On which node to begin search for a page
 *
 * If a task is marked PF_SPREAD_PAGE or PF_SPREAD_SLAB (as for
 * tasks in a cpuset with is_spread_page or is_spread_slab set),
 * and if the memory allocation used cpuset_mem_spread_node()
 * to determine on which node to start looking, as it will for
 * certain page cache or slab cache pages such as used for file
 * system buffers and inode caches, then instead of starting on the
 * local node to look for a free page, rather spread the starting
 * node around the tasks mems_allowed nodes.
 *
 * We don't have to worry about the returned node being offline
 * because "it can't happen", and even if it did, it would be ok.
 *
 * The routines calling guarantee_online_mems() are careful to
 * only set nodes in task->mems_allowed that are online.  So it
 * should not be possible for the following code to return an
 * offline node.  But if it did, that would be ok, as this routine
 * is not returning the node where the allocation must be, only
 * the node where the search should start.  The zonelist passed to
 * __alloc_pages() will include all nodes.  If the slab allocator
 * is passed an offline node, it will fall back to the local node.
 * See kmem_cache_alloc_node().
 */

int cpuset_mem_spread_node(void)
{
        int node;

        node = next_node(current->cpuset_mem_spread_rotor, current->mems_allowed);
        if (node == MAX_NUMNODES)
                node = first_node(current->mems_allowed);
        current->cpuset_mem_spread_rotor = node;
        return node;
}
EXPORT_SYMBOL_GPL(cpuset_mem_spread_node);

/**
 * cpuset_mems_allowed_intersects - Does @tsk1's mems_allowed intersect @tsk2's?
 * @tsk1: pointer to task_struct of some task.
 * @tsk2: pointer to task_struct of some other task.
 *
 * Description: Return true if @tsk1's mems_allowed intersects the
 * mems_allowed of @tsk2.  Used by the OOM killer to determine if
 * one of the task's memory usage might impact the memory available
 * to the other.
 **/

int cpuset_mems_allowed_intersects(const struct task_struct *tsk1,
                                   const struct task_struct *tsk2)
{
        return nodes_intersects(tsk1->mems_allowed, tsk2->mems_allowed);
}

/**
 * cpuset_print_task_mems_allowed - prints task's cpuset and mems_allowed
 * @task: pointer to task_struct of some task.
 *
 * Description: Prints @task's name, cpuset name, and cached copy of its
 * mems_allowed to the kernel log.  Must hold task_lock(task) to allow
 * dereferencing task_cs(task).
 */
void cpuset_print_task_mems_allowed(struct task_struct *tsk)
{
        struct dentry *dentry;

        dentry = task_cs(tsk)->css.cgroup->dentry;
        spin_lock(&cpuset_buffer_lock);
        snprintf(cpuset_name, CPUSET_NAME_LEN,
                 dentry ? (const char *)dentry->d_name.name : "/");
        nodelist_scnprintf(cpuset_nodelist, CPUSET_NODELIST_LEN,
                           tsk->mems_allowed);
        printk(KERN_INFO "%s cpuset=%s mems_allowed=%s\n",
               tsk->comm, cpuset_name, cpuset_nodelist);
        spin_unlock(&cpuset_buffer_lock);
}

/*
 * Collection of memory_pressure is suppressed unless
 * this flag is enabled by writing "1" to the special
 * cpuset file 'memory_pressure_enabled' in the root cpuset.
 */

int cpuset_memory_pressure_enabled __read_mostly;

/**
 * cpuset_memory_pressure_bump - keep stats of per-cpuset reclaims.
 *
 * Keep a running average of the rate of synchronous (direct)
 * page reclaim efforts initiated by tasks in each cpuset.
 *
 * This represents the rate at which some task in the cpuset
 * ran low on memory on all nodes it was allowed to use, and
 * had to enter the kernels page reclaim code in an effort to
 * create more free memory by tossing clean pages or swapping
 * or writing dirty pages.
 *
 * Display to user space in the per-cpuset read-only file
 * "memory_pressure".  Value displayed is an integer
 * representing the recent rate of entry into the synchronous
 * (direct) page reclaim by any task attached to the cpuset.
 **/

void __cpuset_memory_pressure_bump(void)
{
        task_lock(current);
        fmeter_markevent(&task_cs(current)->fmeter);
        task_unlock(current);
}

#ifdef CONFIG_PROC_PID_CPUSET
/*
 * proc_cpuset_show()
 *  - Print tasks cpuset path into seq_file.
 *  - Used for /proc/<pid>/cpuset.
 *  - No need to task_lock(tsk) on this tsk->cpuset reference, as it
 *    doesn't really matter if tsk->cpuset changes after we read it,
 *    and we take cgroup_mutex, keeping cpuset_attach() from changing it
 *    anyway.
 */
static int proc_cpuset_show(struct seq_file *m, void *unused_v)
{
        struct pid *pid;
        struct task_struct *tsk;
        char *buf;
        struct cgroup_subsys_state *css;
        int retval;

        retval = -ENOMEM;
        buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
        if (!buf)
                goto out;

        retval = -ESRCH;
        pid = m->private;
        tsk = get_pid_task(pid, PIDTYPE_PID);
        if (!tsk)
                goto out_free;

        retval = -EINVAL;
        cgroup_lock();
        css = task_subsys_state(tsk, cpuset_subsys_id);
        retval = cgroup_path(css->cgroup, buf, PAGE_SIZE);
        if (retval < 0)
                goto out_unlock;
        seq_puts(m, buf);
        seq_putc(m, '\n');
out_unlock:
        cgroup_unlock();
        put_task_struct(tsk);
out_free:
        kfree(buf);
out:
        return retval;
}

static int cpuset_open(struct inode *inode, struct file *file)
{
        struct pid *pid = PROC_I(inode)->pid;
        return single_open(file, proc_cpuset_show, pid);
}

const struct file_operations proc_cpuset_operations = {
        .open           = cpuset_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = single_release,
};
#endif /* CONFIG_PROC_PID_CPUSET */

/* Display task mems_allowed in /proc/<pid>/status file. */
void cpuset_task_status_allowed(struct seq_file *m, struct task_struct *task)
{
        seq_printf(m, "Mems_allowed:\t");
        seq_nodemask(m, &task->mems_allowed);
        seq_printf(m, "\n");
        seq_printf(m, "Mems_allowed_list:\t");
        seq_nodemask_list(m, &task->mems_allowed);
        seq_printf(m, "\n");
}