cpuset: inherit ancestor's masks if effective_{cpus, mems} becomes empty

[linux-2.6/btrfs-unstable.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/export.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 <linux/atomic.h>
#include <linux/mutex.h>
#include <linux/workqueue.h>
#include <linux/cgroup.h>
#include <linux/wait.h>

struct static_key cpusets_enabled_key __read_mostly = STATIC_KEY_INIT_FALSE;

/* 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 */

        /* user-configured CPUs and Memory Nodes allow to tasks */
        cpumask_var_t cpus_allowed;
        nodemask_t mems_allowed;

        /* effective CPUs and Memory Nodes allow to tasks */
        cpumask_var_t effective_cpus;
        nodemask_t effective_mems;

        /*
         * This is old Memory Nodes tasks took on.
         *
         * - top_cpuset.old_mems_allowed is initialized to mems_allowed.
         * - A new cpuset's old_mems_allowed is initialized when some
         *   task is moved into it.
         * - old_mems_allowed is used in cpuset_migrate_mm() when we change
         *   cpuset.mems_allowed and have tasks' nodemask updated, and
         *   then old_mems_allowed is updated to mems_allowed.
         */
        nodemask_t old_mems_allowed;

        struct fmeter fmeter;           /* memory_pressure filter */

        /*
         * Tasks are being attached to this cpuset.  Used to prevent
         * zeroing cpus/mems_allowed between ->can_attach() and ->attach().
         */
        int attach_in_progress;

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

        /* for custom sched domain */
        int relax_domain_level;
};

static inline struct cpuset *css_cs(struct cgroup_subsys_state *css)
{
        return css ? container_of(css, struct cpuset, css) : NULL;
}

/* Retrieve the cpuset for a task */
static inline struct cpuset *task_cs(struct task_struct *task)
{
        return css_cs(task_css(task, cpuset_cgrp_id));
}

static inline struct cpuset *parent_cs(struct cpuset *cs)
{
        return css_cs(cs->css.parent);
}

#ifdef CONFIG_NUMA
static inline bool task_has_mempolicy(struct task_struct *task)
{
        return task->mempolicy;
}
#else
static inline bool task_has_mempolicy(struct task_struct *task)
{
        return false;
}
#endif


/* bits in struct cpuset flags field */
typedef enum {
        CS_ONLINE,
        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 bool is_cpuset_online(const struct cpuset *cs)
{
        return test_bit(CS_ONLINE, &cs->flags);
}

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_ONLINE) | (1 << CS_CPU_EXCLUSIVE) |
                  (1 << CS_MEM_EXCLUSIVE)),
};

/**
 * cpuset_for_each_child - traverse online children of a cpuset
 * @child_cs: loop cursor pointing to the current child
 * @pos_css: used for iteration
 * @parent_cs: target cpuset to walk children of
 *
 * Walk @child_cs through the online children of @parent_cs.  Must be used
 * with RCU read locked.
 */
#define cpuset_for_each_child(child_cs, pos_css, parent_cs)             \
        css_for_each_child((pos_css), &(parent_cs)->css)                \
                if (is_cpuset_online(((child_cs) = css_cs((pos_css)))))

/**
 * cpuset_for_each_descendant_pre - pre-order walk of a cpuset's descendants
 * @des_cs: loop cursor pointing to the current descendant
 * @pos_css: used for iteration
 * @root_cs: target cpuset to walk ancestor of
 *
 * Walk @des_cs through the online descendants of @root_cs.  Must be used
 * with RCU read locked.  The caller may modify @pos_css by calling
 * css_rightmost_descendant() to skip subtree.  @root_cs is included in the
 * iteration and the first node to be visited.
 */
#define cpuset_for_each_descendant_pre(des_cs, pos_css, root_cs)        \
        css_for_each_descendant_pre((pos_css), &(root_cs)->css)         \
                if (is_cpuset_online(((des_cs) = css_cs((pos_css)))))

/*
 * There are two global mutexes guarding cpuset structures - cpuset_mutex
 * and callback_mutex.  The latter may nest inside the former.  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
 * cpuset_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 cpuset_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(cpuset_mutex);
static DEFINE_MUTEX(callback_mutex);

/*
 * CPU / memory hotplug is handled asynchronously.
 */
static void cpuset_hotplug_workfn(struct work_struct *work);
static DECLARE_WORK(cpuset_hotplug_work, cpuset_hotplug_workfn);

static DECLARE_WAIT_QUEUE_HEAD(cpuset_attach_wq);

/*
 * 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 struct dentry *cpuset_mount(struct file_system_type *fs_type,
                         int flags, const char *unused_dev_name, void *data)
{
        struct file_system_type *cgroup_fs = get_fs_type("cgroup");
        struct dentry *ret = ERR_PTR(-ENODEV);
        if (cgroup_fs) {
                char mountopts[] =
                        "cpuset,noprefix,"
                        "release_agent=/sbin/cpuset_release_agent";
                ret = cgroup_fs->mount(cgroup_fs, flags,
                                           unused_dev_name, mountopts);
                put_filesystem(cgroup_fs);
        }
        return ret;
}

static struct file_system_type cpuset_fs_type = {
        .name = "cpuset",
        .mount = cpuset_mount,
};

/*
 * 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.  The top
 * cpuset always has some cpus online.
 *
 * One way or another, we guarantee to return some non-empty subset
 * of cpu_online_mask.
 *
 * Call with callback_mutex held.
 */
static void guarantee_online_cpus(struct cpuset *cs, struct cpumask *pmask)
{
        while (!cpumask_intersects(cs->cpus_allowed, cpu_online_mask))
                cs = parent_cs(cs);
        cpumask_and(pmask, cs->cpus_allowed, 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.  The top cpuset always has some mems online.
 *
 * One way or another, we guarantee to return some non-empty subset
 * of node_states[N_MEMORY].
 *
 * Call with callback_mutex held.
 */
static void guarantee_online_mems(struct cpuset *cs, nodemask_t *pmask)
{
        while (!nodes_intersects(cs->mems_allowed, node_states[N_MEMORY]))
                cs = parent_cs(cs);
        nodes_and(*pmask, cs->mems_allowed, node_states[N_MEMORY]);
}

/*
 * update task's spread flag if cpuset's page/slab spread flag is set
 *
 * Called with callback_mutex/cpuset_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 cpuset_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(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))
                goto free_cs;
        if (!alloc_cpumask_var(&trial->effective_cpus, GFP_KERNEL))
                goto free_cpus;

        cpumask_copy(trial->cpus_allowed, cs->cpus_allowed);
        cpumask_copy(trial->effective_cpus, cs->effective_cpus);
        return trial;

free_cpus:
        free_cpumask_var(trial->cpus_allowed);
free_cs:
        kfree(trial);
        return NULL;
}

/**
 * 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->effective_cpus);
        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
 * cpuset_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(struct cpuset *cur, struct cpuset *trial)
{
        struct cgroup_subsys_state *css;
        struct cpuset *c, *par;
        int ret;

        rcu_read_lock();

        /* Each of our child cpusets must be a subset of us */
        ret = -EBUSY;
        cpuset_for_each_child(c, css, cur)
                if (!is_cpuset_subset(c, trial))
                        goto out;

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

        par = parent_cs(cur);

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

        /*
         * If either I or some sibling (!= me) is exclusive, we can't
         * overlap
         */
        ret = -EINVAL;
        cpuset_for_each_child(c, css, par) {
                if ((is_cpu_exclusive(trial) || is_cpu_exclusive(c)) &&
                    c != cur &&
                    cpumask_intersects(trial->cpus_allowed, c->cpus_allowed))
                        goto out;
                if ((is_mem_exclusive(trial) || is_mem_exclusive(c)) &&
                    c != cur &&
                    nodes_intersects(trial->mems_allowed, c->mems_allowed))
                        goto out;
        }

        /*
         * Cpusets with tasks - existing or newly being attached - can't
         * be changed to have empty cpus_allowed or mems_allowed.
         */
        ret = -ENOSPC;
        if ((cgroup_has_tasks(cur->css.cgroup) || cur->attach_in_progress)) {
                if (!cpumask_empty(cur->cpus_allowed) &&
                    cpumask_empty(trial->cpus_allowed))
                        goto out;
                if (!nodes_empty(cur->mems_allowed) &&
                    nodes_empty(trial->mems_allowed))
                        goto out;
        }

        ret = 0;
out:
        rcu_read_unlock();
        return ret;
}

#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 *root_cs)
{
        struct cpuset *cp;
        struct cgroup_subsys_state *pos_css;

        rcu_read_lock();
        cpuset_for_each_descendant_pre(cp, pos_css, root_cs) {
                if (cp == root_cs)
                        continue;

                /* skip the whole subtree if @cp doesn't have any CPU */
                if (cpumask_empty(cp->cpus_allowed)) {
                        pos_css = css_rightmost_descendant(pos_css);
                        continue;
                }

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

/*
 * 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/core.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 cpuset_mutex 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/core.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)
{
        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 */
        struct cgroup_subsys_state *pos_css;

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

        rcu_read_lock();
        cpuset_for_each_descendant_pre(cp, pos_css, &top_cpuset) {
                if (cp == &top_cpuset)
                        continue;
                /*
                 * Continue traversing beyond @cp iff @cp has some CPUs and
                 * isn't load balancing.  The former is obvious.  The
                 * latter: 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 (!cpumask_empty(cp->cpus_allowed) &&
                    !is_sched_load_balance(cp))
                        continue;

                if (is_sched_load_balance(cp))
                        csa[csn++] = cp;

                /* skip @cp's subtree */
                pos_css = css_rightmost_descendant(pos_css);
        }
        rcu_read_unlock();

        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) {
                                pr_warn("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.
 *
 * 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.
 *
 * Call with cpuset_mutex held.  Takes get_online_cpus().
 */
static void rebuild_sched_domains_locked(void)
{
        struct sched_domain_attr *attr;
        cpumask_var_t *doms;
        int ndoms;

        lockdep_assert_held(&cpuset_mutex);
        get_online_cpus();

        /*
         * We have raced with CPU hotplug. Don't do anything to avoid
         * passing doms with offlined cpu to partition_sched_domains().
         * Anyways, hotplug work item will rebuild sched domains.
         */
        if (!cpumask_equal(top_cpuset.cpus_allowed, cpu_active_mask))
                goto out;

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

        /* Have scheduler rebuild the domains */
        partition_sched_domains(ndoms, doms, attr);
out:
        put_online_cpus();
}
#else /* !CONFIG_SMP */
static void rebuild_sched_domains_locked(void)
{
}
#endif /* CONFIG_SMP */

void rebuild_sched_domains(void)
{
        mutex_lock(&cpuset_mutex);
        rebuild_sched_domains_locked();
        mutex_unlock(&cpuset_mutex);
}

/*
 * effective_cpumask_cpuset - return nearest ancestor with non-empty cpus
 * @cs: the cpuset in interest
 *
 * A cpuset's effective cpumask is the cpumask of the nearest ancestor
 * with non-empty cpus. We use effective cpumask whenever:
 * - we update tasks' cpus_allowed. (they take on the ancestor's cpumask
 *   if the cpuset they reside in has no cpus)
 * - we want to retrieve task_cs(tsk)'s cpus_allowed.
 *
 * Called with cpuset_mutex held. cpuset_cpus_allowed_fallback() is an
 * exception. See comments there.
 */
static struct cpuset *effective_cpumask_cpuset(struct cpuset *cs)
{
        while (cpumask_empty(cs->cpus_allowed))
                cs = parent_cs(cs);
        return cs;
}

/*
 * effective_nodemask_cpuset - return nearest ancestor with non-empty mems
 * @cs: the cpuset in interest
 *
 * A cpuset's effective nodemask is the nodemask of the nearest ancestor
 * with non-empty memss. We use effective nodemask whenever:
 * - we update tasks' mems_allowed. (they take on the ancestor's nodemask
 *   if the cpuset they reside in has no mems)
 * - we want to retrieve task_cs(tsk)'s mems_allowed.
 *
 * Called with cpuset_mutex held.
 */
static struct cpuset *effective_nodemask_cpuset(struct cpuset *cs)
{
        while (nodes_empty(cs->mems_allowed))
                cs = parent_cs(cs);
        return cs;
}

/**
 * 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
 *
 * Iterate through each task of @cs updating its cpus_allowed to the
 * effective cpuset's.  As this function is called with cpuset_mutex held,
 * cpuset membership stays stable.
 */
static void update_tasks_cpumask(struct cpuset *cs)
{
        struct cpuset *cpus_cs = effective_cpumask_cpuset(cs);
        struct css_task_iter it;
        struct task_struct *task;

        css_task_iter_start(&cs->css, &it);
        while ((task = css_task_iter_next(&it)))
                set_cpus_allowed_ptr(task, cpus_cs->cpus_allowed);
        css_task_iter_end(&it);
}

/*
 * update_cpumasks_hier - Update effective cpumasks and tasks in the subtree
 * @cs: the cpuset to consider
 * @new_cpus: temp variable for calculating new effective_cpus
 *
 * When congifured cpumask is changed, the effective cpumasks of this cpuset
 * and all its descendants need to be updated.
 *
 * On legacy hierachy, effective_cpus will be the same with cpu_allowed.
 *
 * Called with cpuset_mutex held
 */
static void update_cpumasks_hier(struct cpuset *cs, struct cpumask *new_cpus)
{
        struct cpuset *cp;
        struct cgroup_subsys_state *pos_css;

        rcu_read_lock();
        cpuset_for_each_descendant_pre(cp, pos_css, cs) {
                struct cpuset *parent = parent_cs(cp);

                cpumask_and(new_cpus, cp->cpus_allowed, parent->effective_cpus);

                /*
                 * If it becomes empty, inherit the effective mask of the
                 * parent, which is guaranteed to have some CPUs.
                 */
                if (cpumask_empty(new_cpus))
                        cpumask_copy(new_cpus, parent->effective_cpus);

                /* Skip the whole subtree if the cpumask remains the same. */
                if (cpumask_equal(new_cpus, cp->effective_cpus)) {
                        pos_css = css_rightmost_descendant(pos_css);
                        continue;
                }

                if (!css_tryget_online(&cp->css))
                        continue;
                rcu_read_unlock();

                mutex_lock(&callback_mutex);
                cpumask_copy(cp->effective_cpus, new_cpus);
                mutex_unlock(&callback_mutex);

                WARN_ON(!cgroup_on_dfl(cp->css.cgroup) &&
                        !cpumask_equal(cp->cpus_allowed, cp->effective_cpus));

                update_tasks_cpumask(cp);

                rcu_read_lock();
                css_put(&cp->css);
        }
        rcu_read_unlock();
}

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

        /* top_cpuset.cpus_allowed tracks cpu_online_mask; 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;
        }

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

        retval = validate_change(cs, trialcs);
        if (retval < 0)
                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);

        /* use trialcs->cpus_allowed as a temp variable */
        update_cpumasks_hier(cs, trialcs->cpus_allowed);

        if (is_load_balanced)
                rebuild_sched_domains_locked();
        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.
 *
 *    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;
        struct cpuset *mems_cs;

        tsk->mems_allowed = *to;

        do_migrate_pages(mm, from, to, MPOL_MF_MOVE_ALL);

        rcu_read_lock();
        mems_cs = effective_nodemask_cpuset(task_cs(tsk));
        guarantee_online_mems(mems_cs, &tsk->mems_allowed);
        rcu_read_unlock();
}

/*
 * 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.
 */
static void cpuset_change_task_nodemask(struct task_struct *tsk,
                                        nodemask_t *newmems)
{
        bool need_loop;

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

        task_lock(tsk);
        /*
         * Determine if a loop is necessary if another thread is doing
         * read_mems_allowed_begin().  If at least one node remains unchanged and
         * tsk does not have a mempolicy, then an empty nodemask will not be
         * possible when mems_allowed is larger than a word.
         */
        need_loop = task_has_mempolicy(tsk) ||
                        !nodes_intersects(*newmems, tsk->mems_allowed);

        if (need_loop) {
                local_irq_disable();
                write_seqcount_begin(&tsk->mems_allowed_seq);
        }

        nodes_or(tsk->mems_allowed, tsk->mems_allowed, *newmems);
        mpol_rebind_task(tsk, newmems, MPOL_REBIND_STEP1);

        mpol_rebind_task(tsk, newmems, MPOL_REBIND_STEP2);
        tsk->mems_allowed = *newmems;

        if (need_loop) {
                write_seqcount_end(&tsk->mems_allowed_seq);
                local_irq_enable();
        }

        task_unlock(tsk);
}

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
 *
 * Iterate through each task of @cs updating its mems_allowed to the
 * effective cpuset's.  As this function is called with cpuset_mutex held,
 * cpuset membership stays stable.
 */
static void update_tasks_nodemask(struct cpuset *cs)
{
        static nodemask_t newmems;      /* protected by cpuset_mutex */
        struct cpuset *mems_cs = effective_nodemask_cpuset(cs);
        struct css_task_iter it;
        struct task_struct *task;

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

        guarantee_online_mems(mems_cs, &newmems);

        /*
         * 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 cpuset_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.
         */
        css_task_iter_start(&cs->css, &it);
        while ((task = css_task_iter_next(&it))) {
                struct mm_struct *mm;
                bool migrate;

                cpuset_change_task_nodemask(task, &newmems);

                mm = get_task_mm(task);
                if (!mm)
                        continue;

                migrate = is_memory_migrate(cs);

                mpol_rebind_mm(mm, &cs->mems_allowed);
                if (migrate)
                        cpuset_migrate_mm(mm, &cs->old_mems_allowed, &newmems);
                mmput(mm);
        }
        css_task_iter_end(&it);

        /*
         * All the tasks' nodemasks have been updated, update
         * cs->old_mems_allowed.
         */
        cs->old_mems_allowed = newmems;

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

/*
 * update_nodemasks_hier - Update effective nodemasks and tasks in the subtree
 * @cs: the cpuset to consider
 * @new_mems: a temp variable for calculating new effective_mems
 *
 * When configured nodemask is changed, the effective nodemasks of this cpuset
 * and all its descendants need to be updated.
 *
 * On legacy hiearchy, effective_mems will be the same with mems_allowed.
 *
 * Called with cpuset_mutex held
 */
static void update_nodemasks_hier(struct cpuset *cs, nodemask_t *new_mems)
{
        struct cpuset *cp;
        struct cgroup_subsys_state *pos_css;

        rcu_read_lock();
        cpuset_for_each_descendant_pre(cp, pos_css, cs) {
                struct cpuset *parent = parent_cs(cp);

                nodes_and(*new_mems, cp->mems_allowed, parent->effective_mems);

                /*
                 * If it becomes empty, inherit the effective mask of the
                 * parent, which is guaranteed to have some MEMs.
                 */
                if (nodes_empty(*new_mems))
                        *new_mems = parent->effective_mems;

                /* Skip the whole subtree if the nodemask remains the same. */
                if (nodes_equal(*new_mems, cp->effective_mems)) {
                        pos_css = css_rightmost_descendant(pos_css);
                        continue;
                }

                if (!css_tryget_online(&cp->css))
                        continue;
                rcu_read_unlock();

                mutex_lock(&callback_mutex);
                cp->effective_mems = *new_mems;
                mutex_unlock(&callback_mutex);

                WARN_ON(!cgroup_on_dfl(cp->css.cgroup) &&
                        nodes_equal(cp->mems_allowed, cp->effective_mems));

                update_tasks_nodemask(cp);

                rcu_read_lock();
                css_put(&cp->css);
        }
        rcu_read_unlock();
}

/*
 * 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 cpuset_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)
{
        int retval;

        /*
         * top_cpuset.mems_allowed tracks node_stats[N_MEMORY];
         * it's read-only
         */
        if (cs == &top_cpuset) {
                retval = -EACCES;
                goto done;
        }

        /*
         * 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_MEMORY])) {
                        retval =  -EINVAL;
                        goto done;
                }
        }

        if (nodes_equal(cs->mems_allowed, trialcs->mems_allowed)) {
                retval = 0;             /* Too easy - nothing to do */
                goto done;
        }
        retval = validate_change(cs, trialcs);
        if (retval < 0)
                goto done;

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

        /* use trialcs->mems_allowed as a temp variable */
        update_nodemasks_hier(cs, &cs->mems_allowed);
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 >= sched_domain_level_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))
                        rebuild_sched_domains_locked();
        }

        return 0;
}

/**
 * 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
 *
 * Iterate through each task of @cs updating its spread flags.  As this
 * function is called with cpuset_mutex held, cpuset membership stays
 * stable.
 */
static void update_tasks_flags(struct cpuset *cs)
{
        struct css_task_iter it;
        struct task_struct *task;

        css_task_iter_start(&cs->css, &it);
        while ((task = css_task_iter_next(&it)))
                cpuset_update_task_spread_flag(cs, task);
        css_task_iter_end(&it);
}

/*
 * 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 cpuset_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;
        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;

        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)
                rebuild_sched_domains_locked();

        if (spread_flag_changed)
                update_tasks_flags(cs);
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;
}

static struct cpuset *cpuset_attach_old_cs;

/* Called by cgroups to determine if a cpuset is usable; cpuset_mutex held */
static int cpuset_can_attach(struct cgroup_subsys_state *css,
                             struct cgroup_taskset *tset)
{
        struct cpuset *cs = css_cs(css);
        struct task_struct *task;
        int ret;

        /* used later by cpuset_attach() */
        cpuset_attach_old_cs = task_cs(cgroup_taskset_first(tset));

        mutex_lock(&cpuset_mutex);

        /* allow moving tasks into an empty cpuset if on default hierarchy */
        ret = -ENOSPC;
        if (!cgroup_on_dfl(css->cgroup) &&
            (cpumask_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed)))
                goto out_unlock;

        cgroup_taskset_for_each(task, tset) {
                /*
                 * Kthreads which disallow setaffinity shouldn't be moved
                 * to a new cpuset; we don't want to 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.
                 */
                ret = -EINVAL;
                if (task->flags & PF_NO_SETAFFINITY)
                        goto out_unlock;
                ret = security_task_setscheduler(task);
                if (ret)
                        goto out_unlock;
        }

        /*
         * Mark attach is in progress.  This makes validate_change() fail
         * changes which zero cpus/mems_allowed.
         */
        cs->attach_in_progress++;
        ret = 0;
out_unlock:
        mutex_unlock(&cpuset_mutex);
        return ret;
}

static void cpuset_cancel_attach(struct cgroup_subsys_state *css,
                                 struct cgroup_taskset *tset)
{
        mutex_lock(&cpuset_mutex);
        css_cs(css)->attach_in_progress--;
        mutex_unlock(&cpuset_mutex);
}

/*
 * Protected by cpuset_mutex.  cpus_attach is used only by cpuset_attach()
 * but we can't allocate it dynamically there.  Define it global and
 * allocate from cpuset_init().
 */
static cpumask_var_t cpus_attach;

static void cpuset_attach(struct cgroup_subsys_state *css,
                          struct cgroup_taskset *tset)
{
        /* static buf protected by cpuset_mutex */
        static nodemask_t cpuset_attach_nodemask_to;
        struct mm_struct *mm;
        struct task_struct *task;
        struct task_struct *leader = cgroup_taskset_first(tset);
        struct cpuset *cs = css_cs(css);
        struct cpuset *oldcs = cpuset_attach_old_cs;
        struct cpuset *cpus_cs = effective_cpumask_cpuset(cs);
        struct cpuset *mems_cs = effective_nodemask_cpuset(cs);

        mutex_lock(&cpuset_mutex);

        /* prepare for attach */
        if (cs == &top_cpuset)
                cpumask_copy(cpus_attach, cpu_possible_mask);
        else
                guarantee_online_cpus(cpus_cs, cpus_attach);

        guarantee_online_mems(mems_cs, &cpuset_attach_nodemask_to);

        cgroup_taskset_for_each(task, tset) {
                /*
                 * can_attach beforehand should guarantee that this doesn't
                 * fail.  TODO: have a better way to handle failure here
                 */
                WARN_ON_ONCE(set_cpus_allowed_ptr(task, cpus_attach));

                cpuset_change_task_nodemask(task, &cpuset_attach_nodemask_to);
                cpuset_update_task_spread_flag(cs, task);
        }

        /*
         * Change mm, possibly for multiple threads in a threadgroup. This is
         * expensive and may sleep.
         */
        cpuset_attach_nodemask_to = cs->mems_allowed;
        mm = get_task_mm(leader);
        if (mm) {
                struct cpuset *mems_oldcs = effective_nodemask_cpuset(oldcs);

                mpol_rebind_mm(mm, &cpuset_attach_nodemask_to);

                /*
                 * old_mems_allowed is the same with mems_allowed here, except
                 * if this task is being moved automatically due to hotplug.
                 * In that case @mems_allowed has been updated and is empty,
                 * so @old_mems_allowed is the right nodesets that we migrate
                 * mm from.
                 */
                if (is_memory_migrate(cs)) {
                        cpuset_migrate_mm(mm, &mems_oldcs->old_mems_allowed,
                                          &cpuset_attach_nodemask_to);
                }
                mmput(mm);
        }

        cs->old_mems_allowed = cpuset_attach_nodemask_to;

        cs->attach_in_progress--;
        if (!cs->attach_in_progress)
                wake_up(&cpuset_attach_wq);

        mutex_unlock(&cpuset_mutex);
}

/* 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_subsys_state *css, struct cftype *cft,
                            u64 val)
{
        struct cpuset *cs = css_cs(css);
        cpuset_filetype_t type = cft->private;
        int retval = 0;

        mutex_lock(&cpuset_mutex);
        if (!is_cpuset_online(cs)) {
                retval = -ENODEV;
                goto out_unlock;
        }

        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;
        }
out_unlock:
        mutex_unlock(&cpuset_mutex);
        return retval;
}

static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft,
                            s64 val)
{
        struct cpuset *cs = css_cs(css);
        cpuset_filetype_t type = cft->private;
        int retval = -ENODEV;

        mutex_lock(&cpuset_mutex);
        if (!is_cpuset_online(cs))
                goto out_unlock;

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

/*
 * Common handling for a write to a "cpus" or "mems" file.
 */
static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
                                    char *buf, size_t nbytes, loff_t off)
{
        struct cpuset *cs = css_cs(of_css(of));
        struct cpuset *trialcs;
        int retval = -ENODEV;

        buf = strstrip(buf);

        /*
         * CPU or memory hotunplug may leave @cs w/o any execution
         * resources, in which case the hotplug code asynchronously updates
         * configuration and transfers all tasks to the nearest ancestor
         * which can execute.
         *
         * As writes to "cpus" or "mems" may restore @cs's execution
         * resources, wait for the previously scheduled operations before
         * proceeding, so that we don't end up keep removing tasks added
         * after execution capability is restored.
         */
        flush_work(&cpuset_hotplug_work);

        mutex_lock(&cpuset_mutex);
        if (!is_cpuset_online(cs))
                goto out_unlock;

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

        switch (of_cft(of)->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_unlock:
        mutex_unlock(&cpuset_mutex);
        return retval ?: nbytes;
}

/*
 * 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.
 */
static int cpuset_common_seq_show(struct seq_file *sf, void *v)
{
        struct cpuset *cs = css_cs(seq_css(sf));
        cpuset_filetype_t type = seq_cft(sf)->private;
        ssize_t count;
        char *buf, *s;
        int ret = 0;

        count = seq_get_buf(sf, &buf);
        s = buf;

        mutex_lock(&callback_mutex);

        switch (type) {
        case FILE_CPULIST:
                s += cpulist_scnprintf(s, count, cs->cpus_allowed);
                break;
        case FILE_MEMLIST:
                s += nodelist_scnprintf(s, count, cs->mems_allowed);
                break;
        default:
                ret = -EINVAL;
                goto out_unlock;
        }

        if (s < buf + count - 1) {
                *s++ = '\n';
                seq_commit(sf, s - buf);
        } else {
                seq_commit(sf, -1);
        }
out_unlock:
        mutex_unlock(&callback_mutex);
        return ret;
}

static u64 cpuset_read_u64(struct cgroup_subsys_state *css, struct cftype *cft)
{
        struct cpuset *cs = css_cs(css);
        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_subsys_state *css, struct cftype *cft)
{
        struct cpuset *cs = css_cs(css);
        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",
                .seq_show = cpuset_common_seq_show,
                .write = cpuset_write_resmask,
                .max_write_len = (100U + 6 * NR_CPUS),
                .private = FILE_CPULIST,
        },

        {
                .name = "mems",
                .seq_show = cpuset_common_seq_show,
                .write = 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,
        },

        {
                .name = "memory_pressure_enabled",
                .flags = CFTYPE_ONLY_ON_ROOT,
                .read_u64 = cpuset_read_u64,
                .write_u64 = cpuset_write_u64,
                .private = FILE_MEMORY_PRESSURE_ENABLED,
        },

        { }     /* terminate */
};

/*
 *      cpuset_css_alloc - allocate a cpuset css
 *      cgrp:   control group that the new cpuset will be part of
 */

static struct cgroup_subsys_state *
cpuset_css_alloc(struct cgroup_subsys_state *parent_css)
{
        struct cpuset *cs;

        if (!parent_css)
                return &top_cpuset.css;

        cs = kzalloc(sizeof(*cs), GFP_KERNEL);
        if (!cs)
                return ERR_PTR(-ENOMEM);
        if (!alloc_cpumask_var(&cs->cpus_allowed, GFP_KERNEL))
                goto free_cs;
        if (!alloc_cpumask_var(&cs->effective_cpus, GFP_KERNEL))
                goto free_cpus;

        set_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
        cpumask_clear(cs->cpus_allowed);
        nodes_clear(cs->mems_allowed);
        cpumask_clear(cs->effective_cpus);
        nodes_clear(cs->effective_mems);
        fmeter_init(&cs->fmeter);
        cs->relax_domain_level = -1;

        return &cs->css;

free_cpus:
        free_cpumask_var(cs->cpus_allowed);
free_cs:
        kfree(cs);
        return ERR_PTR(-ENOMEM);
}

static int cpuset_css_online(struct cgroup_subsys_state *css)
{
        struct cpuset *cs = css_cs(css);
        struct cpuset *parent = parent_cs(cs);
        struct cpuset *tmp_cs;
        struct cgroup_subsys_state *pos_css;

        if (!parent)
                return 0;

        mutex_lock(&cpuset_mutex);

        set_bit(CS_ONLINE, &cs->flags);
        if (is_spread_page(parent))
                set_bit(CS_SPREAD_PAGE, &cs->flags);
        if (is_spread_slab(parent))
                set_bit(CS_SPREAD_SLAB, &cs->flags);

        cpuset_inc();

        mutex_lock(&callback_mutex);
        if (cgroup_on_dfl(cs->css.cgroup)) {
                cpumask_copy(cs->effective_cpus, parent->effective_cpus);
                cs->effective_mems = parent->effective_mems;
        }
        mutex_unlock(&callback_mutex);

        if (!test_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags))
                goto out_unlock;

        /*
         * Clone @parent's configuration if CGRP_CPUSET_CLONE_CHILDREN is
         * set.  This flag handling is implemented in cgroup core for
         * histrical reasons - the flag may be specified during mount.
         *
         * Currently, if any sibling cpusets have exclusive cpus or mem, we
         * refuse to clone the configuration - thereby refusing the task to
         * be entered, and as a result refusing the sys_unshare() or
         * clone() which initiated it.  If this becomes a problem for some
         * users who wish to allow that scenario, then this could be
         * changed to grant parent->cpus_allowed-sibling_cpus_exclusive
         * (and likewise for mems) to the new cgroup.
         */
        rcu_read_lock();
        cpuset_for_each_child(tmp_cs, pos_css, parent) {
                if (is_mem_exclusive(tmp_cs) || is_cpu_exclusive(tmp_cs)) {
                        rcu_read_unlock();
                        goto out_unlock;
                }
        }
        rcu_read_unlock();

        mutex_lock(&callback_mutex);
        cs->mems_allowed = parent->mems_allowed;
        cpumask_copy(cs->cpus_allowed, parent->cpus_allowed);
        mutex_unlock(&callback_mutex);
out_unlock:
        mutex_unlock(&cpuset_mutex);
        return 0;
}

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

static void cpuset_css_offline(struct cgroup_subsys_state *css)
{
        struct cpuset *cs = css_cs(css);

        mutex_lock(&cpuset_mutex);

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

        cpuset_dec();
        clear_bit(CS_ONLINE, &cs->flags);

        mutex_unlock(&cpuset_mutex);
}

static void cpuset_css_free(struct cgroup_subsys_state *css)
{
        struct cpuset *cs = css_cs(css);

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

struct cgroup_subsys cpuset_cgrp_subsys = {
        .css_alloc = cpuset_css_alloc,
        .css_online = cpuset_css_online,
        .css_offline = cpuset_css_offline,
        .css_free = cpuset_css_free,
        .can_attach = cpuset_can_attach,
        .cancel_attach = cpuset_cancel_attach,
        .attach = cpuset_attach,
        .base_cftypes = files,
        .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();
        if (!alloc_cpumask_var(&top_cpuset.effective_cpus, GFP_KERNEL))
                BUG();

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

        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();

        return 0;
}

/*
 * 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.
 */
static void remove_tasks_in_empty_cpuset(struct cpuset *cs)
{
        struct cpuset *parent;

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

        if (cgroup_transfer_tasks(parent->css.cgroup, cs->css.cgroup)) {
                pr_err("cpuset: failed to transfer tasks out of empty cpuset ");
                pr_cont_cgroup_name(cs->css.cgroup);
                pr_cont("\n");
        }
}

/**
 * cpuset_hotplug_update_tasks - update tasks in a cpuset for hotunplug
 * @cs: cpuset in interest
 *
 * Compare @cs's cpu and mem masks against top_cpuset and if some have gone
 * offline, update @cs accordingly.  If @cs ends up with no CPU or memory,
 * all its tasks are moved to the nearest ancestor with both resources.
 */
static void cpuset_hotplug_update_tasks(struct cpuset *cs)
{
        static cpumask_t off_cpus;
        static nodemask_t off_mems;
        bool is_empty;
        bool on_dfl = cgroup_on_dfl(cs->css.cgroup);

retry:
        wait_event(cpuset_attach_wq, cs->attach_in_progress == 0);

        mutex_lock(&cpuset_mutex);

        /*
         * We have raced with task attaching. We wait until attaching
         * is finished, so we won't attach a task to an empty cpuset.
         */
        if (cs->attach_in_progress) {
                mutex_unlock(&cpuset_mutex);
                goto retry;
        }

        cpumask_andnot(&off_cpus, cs->cpus_allowed, top_cpuset.cpus_allowed);
        nodes_andnot(off_mems, cs->mems_allowed, top_cpuset.mems_allowed);

        mutex_lock(&callback_mutex);
        cpumask_andnot(cs->cpus_allowed, cs->cpus_allowed, &off_cpus);

        /* Inherit the effective mask of the parent, if it becomes empty. */
        cpumask_andnot(cs->effective_cpus, cs->effective_cpus, &off_cpus);
        if (on_dfl && cpumask_empty(cs->effective_cpus))
                cpumask_copy(cs->effective_cpus, parent_cs(cs)->effective_cpus);
        mutex_unlock(&callback_mutex);

        /*
         * If on_dfl, we need to update tasks' cpumask for empty cpuset to
         * take on ancestor's cpumask. Otherwise, don't call
         * update_tasks_cpumask() if the cpuset becomes empty, as the tasks
         * in it will be migrated to an ancestor.
         */
        if ((on_dfl && cpumask_empty(cs->cpus_allowed)) ||
            (!cpumask_empty(&off_cpus) && !cpumask_empty(cs->cpus_allowed)))
                update_tasks_cpumask(cs);

        mutex_lock(&callback_mutex);
        nodes_andnot(cs->mems_allowed, cs->mems_allowed, off_mems);

        /* Inherit the effective mask of the parent, if it becomes empty */
        nodes_andnot(cs->effective_mems, cs->effective_mems, off_mems);
        if (on_dfl && nodes_empty(cs->effective_mems))
                cs->effective_mems = parent_cs(cs)->effective_mems;
        mutex_unlock(&callback_mutex);

        /*
         * If on_dfl, we need to update tasks' nodemask for empty cpuset to
         * take on ancestor's nodemask. Otherwise, don't call
         * update_tasks_nodemask() if the cpuset becomes empty, as the
         * tasks in it will be migratd to an ancestor.
         */
        if ((on_dfl && nodes_empty(cs->mems_allowed)) ||
            (!nodes_empty(off_mems) && !nodes_empty(cs->mems_allowed)))
                update_tasks_nodemask(cs);

        is_empty = cpumask_empty(cs->cpus_allowed) ||
                nodes_empty(cs->mems_allowed);

        mutex_unlock(&cpuset_mutex);

        /*
         * If on_dfl, we'll keep tasks in empty cpusets.
         *
         * Otherwise move tasks to the nearest ancestor with execution
         * resources.  This is full cgroup operation which will
         * also call back into cpuset.  Should be done outside any lock.
         */
        if (!on_dfl && is_empty)
                remove_tasks_in_empty_cpuset(cs);
}

/**
 * cpuset_hotplug_workfn - handle CPU/memory hotunplug for a cpuset
 *
 * This function is called after either CPU or memory configuration has
 * changed and updates cpuset accordingly.  The top_cpuset is always
 * synchronized to cpu_active_mask and N_MEMORY, which 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.
 *
 * Non-root cpusets are only affected by offlining.  If any CPUs or memory
 * nodes have been taken down, cpuset_hotplug_update_tasks() is invoked on
 * all descendants.
 *
 * Note that CPU offlining during suspend is ignored.  We don't modify
 * cpusets across suspend/resume cycles at all.
 */
static void cpuset_hotplug_workfn(struct work_struct *work)
{
        static cpumask_t new_cpus;
        static nodemask_t new_mems;
        bool cpus_updated, mems_updated;

        mutex_lock(&cpuset_mutex);

        /* fetch the available cpus/mems and find out which changed how */
        cpumask_copy(&new_cpus, cpu_active_mask);
        new_mems = node_states[N_MEMORY];

        cpus_updated = !cpumask_equal(top_cpuset.cpus_allowed, &new_cpus);
        mems_updated = !nodes_equal(top_cpuset.mems_allowed, new_mems);

        /* synchronize cpus_allowed to cpu_active_mask */
        if (cpus_updated) {
                mutex_lock(&callback_mutex);
                cpumask_copy(top_cpuset.cpus_allowed, &new_cpus);
                cpumask_copy(top_cpuset.effective_cpus, &new_cpus);
                mutex_unlock(&callback_mutex);
                /* we don't mess with cpumasks of tasks in top_cpuset */
        }

        /* synchronize mems_allowed to N_MEMORY */
        if (mems_updated) {
                mutex_lock(&callback_mutex);
                top_cpuset.mems_allowed = new_mems;
                top_cpuset.effective_mems = new_mems;
                mutex_unlock(&callback_mutex);
                update_tasks_nodemask(&top_cpuset);
        }

        mutex_unlock(&cpuset_mutex);

        /* if cpus or mems changed, we need to propagate to descendants */
        if (cpus_updated || mems_updated) {
                struct cpuset *cs;
                struct cgroup_subsys_state *pos_css;

                rcu_read_lock();
                cpuset_for_each_descendant_pre(cs, pos_css, &top_cpuset) {
                        if (cs == &top_cpuset || !css_tryget_online(&cs->css))
                                continue;
                        rcu_read_unlock();

                        cpuset_hotplug_update_tasks(cs);

                        rcu_read_lock();
                        css_put(&cs->css);
                }
                rcu_read_unlock();
        }

        /* rebuild sched domains if cpus_allowed has changed */
        if (cpus_updated)
                rebuild_sched_domains();
}

void cpuset_update_active_cpus(bool cpu_online)
{
        /*
         * We're inside cpu hotplug critical region which usually nests
         * inside cgroup synchronization.  Bounce actual hotplug processing
         * to a work item to avoid reverse locking order.
         *
         * We still need to do partition_sched_domains() synchronously;
         * otherwise, the scheduler will get confused and put tasks to the
         * dead CPU.  Fall back to the default single domain.
         * cpuset_hotplug_workfn() will rebuild it as necessary.
         */
        partition_sched_domains(1, NULL, NULL);
        schedule_work(&cpuset_hotplug_work);
}

/*
 * Keep top_cpuset.mems_allowed tracking node_states[N_MEMORY].
 * Call this routine anytime after node_states[N_MEMORY] changes.
 * See cpuset_update_active_cpus() for CPU hotplug handling.
 */
static int cpuset_track_online_nodes(struct notifier_block *self,
                                unsigned long action, void *arg)
{
        schedule_work(&cpuset_hotplug_work);
        return NOTIFY_OK;
}

static struct notifier_block cpuset_track_online_nodes_nb = {
        .notifier_call = cpuset_track_online_nodes,
        .priority = 10,         /* ??! */
};

/**
 * 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_MEMORY];
        top_cpuset.old_mems_allowed = top_cpuset.mems_allowed;

        cpumask_copy(top_cpuset.effective_cpus, cpu_active_mask);
        top_cpuset.effective_mems = node_states[N_MEMORY];

        register_hotmemory_notifier(&cpuset_track_online_nodes_nb);
}

/**
 * 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_mask, even if this means going outside the
 * tasks cpuset.
 **/

void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
{
        struct cpuset *cpus_cs;

        mutex_lock(&callback_mutex);
        rcu_read_lock();
        cpus_cs = effective_cpumask_cpuset(task_cs(tsk));
        guarantee_online_cpus(cpus_cs, pmask);
        rcu_read_unlock();
        mutex_unlock(&callback_mutex);
}

void cpuset_cpus_allowed_fallback(struct task_struct *tsk)
{
        struct cpuset *cpus_cs;

        rcu_read_lock();
        cpus_cs = effective_cpumask_cpuset(task_cs(tsk));
        do_set_cpus_allowed(tsk, cpus_cs->cpus_allowed);
        rcu_read_unlock();

        /*
         * We own tsk->cpus_allowed, nobody can change it under us.
         *
         * But we used cs && cs->cpus_allowed lockless and thus can
         * race with cgroup_attach_task() or update_cpumask() and get
         * the wrong tsk->cpus_allowed. However, both cases imply the
         * subsequent cpuset_change_cpumask()->set_cpus_allowed_ptr()
         * which takes task_rq_lock().
         *
         * If we are called after it dropped the lock we must see all
         * changes in tsk_cs()->cpus_allowed. Otherwise we can temporary
         * set any mask even if it is not right from task_cs() pov,
         * the pending set_cpus_allowed_ptr() will fix things.
         *
         * select_fallback_rq() will fix things ups and set cpu_possible_mask
         * if required.
         */
}

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_MEMORY], even if this means going outside the
 * tasks cpuset.
 **/

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

        mutex_lock(&callback_mutex);
        rcu_read_lock();
        mems_cs = effective_nodemask_cpuset(task_cs(tsk));
        guarantee_online_mems(mems_cs, &mask);
        rcu_read_unlock();
        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 struct cpuset *nearest_hardwall_ancestor(struct cpuset *cs)
{
        while (!(is_mem_exclusive(cs) || is_mem_hardwall(cs)) && parent_cs(cs))
                cs = parent_cs(cs);
        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)
{
        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);

        rcu_read_lock();
        cs = nearest_hardwall_ancestor(task_cs(current));
        allowed = node_isset(node, cs->mems_allowed);
        rcu_read_unlock();

        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_mem_spread_node() - On which node to begin search for a file page
 * cpuset_slab_spread_node() - On which node to begin search for a slab 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().
 */

static int cpuset_spread_node(int *rotor)
{
        int node;

        node = next_node(*rotor, current->mems_allowed);
        if (node == MAX_NUMNODES)
                node = first_node(current->mems_allowed);
        *rotor = node;
        return node;
}

int cpuset_mem_spread_node(void)
{
        if (current->cpuset_mem_spread_rotor == NUMA_NO_NODE)
                current->cpuset_mem_spread_rotor =
                        node_random(&current->mems_allowed);

        return cpuset_spread_node(&current->cpuset_mem_spread_rotor);
}

int cpuset_slab_spread_node(void)
{
        if (current->cpuset_slab_spread_rotor == NUMA_NO_NODE)
                current->cpuset_slab_spread_rotor =
                        node_random(&current->mems_allowed);

        return cpuset_spread_node(&current->cpuset_slab_spread_rotor);
}

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);
}

#define CPUSET_NODELIST_LEN     (256)

/**
 * cpuset_print_task_mems_allowed - prints task's cpuset and mems_allowed
 * @tsk: 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.
 */
void cpuset_print_task_mems_allowed(struct task_struct *tsk)
{
         /* Statically allocated to prevent using excess stack. */
        static char cpuset_nodelist[CPUSET_NODELIST_LEN];
        static DEFINE_SPINLOCK(cpuset_buffer_lock);
        struct cgroup *cgrp;

        spin_lock(&cpuset_buffer_lock);
        rcu_read_lock();

        cgrp = task_cs(tsk)->css.cgroup;
        nodelist_scnprintf(cpuset_nodelist, CPUSET_NODELIST_LEN,
                           tsk->mems_allowed);
        pr_info("%s cpuset=", tsk->comm);
        pr_cont_cgroup_name(cgrp);
        pr_cont(" mems_allowed=%s\n", cpuset_nodelist);

        rcu_read_unlock();
        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)
{
        rcu_read_lock();
        fmeter_markevent(&task_cs(current)->fmeter);
        rcu_read_unlock();
}

#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 cpuset_mutex, keeping cpuset_attach() from changing it
 *    anyway.
 */
int proc_cpuset_show(struct seq_file *m, void *unused_v)
{
        struct pid *pid;
        struct task_struct *tsk;
        char *buf, *p;
        struct cgroup_subsys_state *css;
        int retval;

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

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

        retval = -ENAMETOOLONG;
        rcu_read_lock();
        css = task_css(tsk, cpuset_cgrp_id);
        p = cgroup_path(css->cgroup, buf, PATH_MAX);
        rcu_read_unlock();
        if (!p)
                goto out_put_task;
        seq_puts(m, p);
        seq_putc(m, '\n');
        retval = 0;
out_put_task:
        put_task_struct(tsk);
out_free:
        kfree(buf);
out:
        return retval;
}
#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_puts(m, "Mems_allowed:\t");
        seq_nodemask(m, &task->mems_allowed);
        seq_puts(m, "\n");
        seq_puts(m, "Mems_allowed_list:\t");
        seq_nodemask_list(m, &task->mems_allowed);
        seq_puts(m, "\n");
}