kernel/cgroup/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/fs_context.h>
#include <linux/namei.h>
#include <linux/pagemap.h>
#include <linux/proc_fs.h>
#include <linux/rcupdate.h>
#include <linux/sched.h>
#include <linux/sched/deadline.h>
#include <linux/sched/mm.h>
#include <linux/sched/task.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/time64.h>
#include <linux/backing-dev.h>
#include <linux/sort.h>
#include <linux/oom.h>
#include <linux/sched/isolation.h>
#include <linux/uaccess.h>
#include <linux/atomic.h>
#include <linux/mutex.h>
#include <linux/cgroup.h>
#include <linux/wait.h>

DEFINE_STATIC_KEY_FALSE(cpusets_pre_enable_key);
DEFINE_STATIC_KEY_FALSE(cpusets_enabled_key);

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

struct fmeter {
    int cnt;         /* unprocessed events count */
    int val;         /* most recent output value */
    time64_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 */

    /*
     * On default hierarchy:
     *
     * The user-configured masks can only be changed by writing to
     * cpuset.cpus and cpuset.mems, and won't be limited by the
     * parent masks.
     *
     * The effective masks is the real masks that apply to the tasks
     * in the cpuset. They may be changed if the configured masks are
     * changed or hotplug happens.
     *
     * effective_mask == configured_mask & parent's effective_mask,
     * and if it ends up empty, it will inherit the parent's mask.
     *
     *
     * On legacy hierachy:
     *
     * The user-configured masks are always the same with effective masks.
     */

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

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

    /*
     * CPUs allocated to child sub-partitions (default hierarchy only)
     * - CPUs granted by the parent = effective_cpus U subparts_cpus
     * - effective_cpus and subparts_cpus are mutually exclusive.
     *
     * effective_cpus contains only onlined CPUs, but subparts_cpus
     * may have offlined ones.
     */
    cpumask_var_t subparts_cpus;

    /*
     * 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;

    /* number of CPUs in subparts_cpus */
    int nr_subparts_cpus;

    /* partition root state */
    int partition_root_state;

    /*
     * Default hierarchy only:
     * use_parent_ecpus - set if using parent's effective_cpus
     * child_ecpus_count - # of children with use_parent_ecpus set
     */
    int use_parent_ecpus;
    int child_ecpus_count;
};

/*
 * Partition root states:
 *
 *   0 - not a partition root
 *
 *   1 - partition root
 *
 *  -1 - invalid partition root
 *       None of the cpus in cpus_allowed can be put into the parent's
 *       subparts_cpus. In this case, the cpuset is not a real partition
 *       root anymore.  However, the CPU_EXCLUSIVE bit will still be set
 *       and the cpuset can be restored back to a partition root if the
 *       parent cpuset can give more CPUs back to this child cpuset.
 */
#define PRS_DISABLED 0
#define PRS_ENABLED 1
#define PRS_ERROR (-1)

/*
 * Temporary cpumasks for working with partitions that are passed among
 * functions to avoid memory allocation in inner functions.
 */
struct tmpmasks {
    cpumask_var_t addmask, delmask; /* For partition root */
    cpumask_var_t new_cpus;         /* For update_cpumasks_hier() */
};

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);
}

/* 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(struct cpuset *cs)
{
    return test_bit(CS_ONLINE, &cs->flags) && !css_is_dying(&cs->css);
}

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 inline int is_partition_root(const struct cpuset *cs)
{
    return cs->partition_root_state > 0;
}

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

/**
 * 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 locks guarding cpuset structures - cpuset_mutex and
 * callback_lock. 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 locks 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_lock 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_lock to query cpusets.
 * Once it is ready to make the changes, it takes callback_lock, blocking
 * everyone else.
 *
 * Calls to the kernel memory allocator can not be made while holding
 * callback_lock, as that would risk double tripping on callback_lock
 * from one of the callbacks into the cpuset code from within
 * __alloc_pages().
 *
 * If a task is only holding callback_lock, 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_lock 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);

DEFINE_STATIC_PERCPU_RWSEM(cpuset_rwsem);

void cpuset_read_lock(void)
{
    percpu_down_read(&cpuset_rwsem);
}

void cpuset_read_unlock(void)
{
    percpu_up_read(&cpuset_rwsem);
}

static DEFINE_SPINLOCK(callback_lock);

static struct workqueue_struct *cpuset_migrate_mm_wq;

/*
 * CPU / memory hotplug is handled asynchronously
 * for hotplug, synchronously for resume_cpus
 */
static DECLARE_WORK(cpuset_hotplug_work, cpuset_hotplug_workfn);

static DECLARE_WAIT_QUEUE_HEAD(cpuset_attach_wq);

/*
 * Cgroup v2 behavior is used on the "cpus" and "mems" control files when
 * on default hierarchy or when the cpuset_v2_mode flag is set by mounting
 * the v1 cpuset cgroup filesystem with the "cpuset_v2_mode" mount option.
 * With v2 behavior, "cpus" and "mems" are always what the users have
 * requested and won't be changed by hotplug events. Only the effective
 * cpus or mems will be affected.
 */
static inline bool is_in_v2_mode(void)
{
    return cgroup_subsys_on_dfl(cpuset_cgrp_subsys) || (cpuset_cgrp_subsys.root->flags & CGRP_ROOT_CPUSET_V2_MODE);
}

/*
 * Return in pmask the portion of a task's cpusets's cpus_allowed that
 * are online and are capable of running the task.  If none are found,
 * walk up the cpuset hierarchy until we find one that does have some
 * appropriate cpus.
 *
 * One way or another, we guarantee to return some non-empty subset
 * of cpu_active_mask.
 *
 * Call with callback_lock or cpuset_mutex held.
 */
static void guarantee_online_cpus(struct task_struct *tsk, struct cpumask *pmask)
{
    const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);
    struct cpuset *cs;

    if (WARN_ON(!cpumask_and(pmask, possible_mask, cpu_active_mask))) {
        cpumask_copy(pmask, cpu_active_mask);
    }

    rcu_read_lock();
    cs = task_cs(tsk);

    while (!cpumask_intersects(cs->effective_cpus, pmask)) {
        cs = parent_cs(cs);
        if (unlikely(!cs)) {
            /*
             * The top cpuset doesn't have any online cpu as a
             * consequence of a race between cpuset_hotplug_work
             * and cpu hotplug notifier.  But we know the top
             * cpuset's effective_cpus is on its way to be
             * identical to cpu_online_mask.
             */
            goto out_unlock;
        }
    }
    cpumask_and(pmask, pmask, cs->effective_cpus);

out_unlock:
    rcu_read_unlock();
}

/*
 * 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_lock or cpuset_mutex held.
 */
static void guarantee_online_mems(struct cpuset *cs, nodemask_t *pmask)
{
    while (!nodes_intersects(cs->effective_mems, node_states[N_MEMORY])) {
        cs = parent_cs(cs);
    }
    nodes_and(*pmask, cs->effective_mems, node_states[N_MEMORY]);
}

/*
 * update task's spread flag if cpuset's page/slab spread flag is set
 *
 * Call with callback_lock or cpuset_mutex held.
 */
static void cpuset_update_task_spread_flag(struct cpuset *cs, struct task_struct *tsk)
{
    if (is_spread_page(cs)) {
        task_set_spread_page(tsk);
    } else {
        task_clear_spread_page(tsk);
    }

    if (is_spread_slab(cs)) {
        task_set_spread_slab(tsk);
    } else {
        task_clear_spread_slab(tsk);
    }
}

/*
 * 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_requested, q->cpus_requested) && 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_cpumasks - allocate three cpumasks for cpuset
 * @cs:  the cpuset that have cpumasks to be allocated.
 * @tmp: the tmpmasks structure pointer
 * Return: 0 if successful, -ENOMEM otherwise.
 *
 * Only one of the two input arguments should be non-NULL.
 */
static inline int alloc_cpumasks(struct cpuset *cs, struct tmpmasks *tmp)
{
    cpumask_var_t *pmask1, *pmask2, *pmask3, *pmask4;

    if (cs) {
        pmask1 = &cs->cpus_allowed;
        pmask2 = &cs->effective_cpus;
        pmask3 = &cs->subparts_cpus;
        pmask4 = &cs->cpus_requested;
    } else {
        pmask1 = &tmp->new_cpus;
        pmask2 = &tmp->addmask;
        pmask3 = &tmp->delmask;
    }

    if (!zalloc_cpumask_var(pmask1, GFP_KERNEL)) {
        return -ENOMEM;
    }

    if (!zalloc_cpumask_var(pmask2, GFP_KERNEL)) {
        goto free_one;
    }

    if (!zalloc_cpumask_var(pmask3, GFP_KERNEL)) {
        goto free_two;
    }

    if (cs && !zalloc_cpumask_var(pmask4, GFP_KERNEL)) {
        goto free_three;
    }

    if (cs && !zalloc_cpumask_var(&cs->cpus_requested, GFP_KERNEL)) {
        goto free_three;
    }

    return 0;

free_three:
    free_cpumask_var(*pmask3);
free_two:
    free_cpumask_var(*pmask2);
free_one:
    free_cpumask_var(*pmask1);
    return -ENOMEM;
}

/**
 * free_cpumasks - free cpumasks in a tmpmasks structure
 * @cs:  the cpuset that have cpumasks to be free.
 * @tmp: the tmpmasks structure pointer
 */
static inline void free_cpumasks(struct cpuset *cs, struct tmpmasks *tmp)
{
    if (cs) {
        free_cpumask_var(cs->cpus_allowed);
        free_cpumask_var(cs->cpus_requested);
        free_cpumask_var(cs->effective_cpus);
        free_cpumask_var(cs->subparts_cpus);
    }
    if (tmp) {
        free_cpumask_var(tmp->new_cpus);
        free_cpumask_var(tmp->addmask);
        free_cpumask_var(tmp->delmask);
    }
}

/**
 * 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_cpumasks(trial, NULL)) {
        kfree(trial);
        return NULL;
    }

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

/**
 * free_cpuset - free the cpuset
 * @cs: the cpuset to be freed
 */
static inline void free_cpuset(struct cpuset *cs)
{
    free_cpumasks(cs, NULL);
    kfree(cs);
}

/*
 * 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);

    /* On legacy hiearchy, we must be a subset of our parent cpuset. */
    ret = -EACCES;
    if (!is_in_v2_mode() && !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_requested, c->cpus_requested)) {
            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_is_populated(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;
        }
    }

    /*
     * We can't shrink if we won't have enough room for SCHED_DEADLINE
     * tasks.
     */
    ret = -EBUSY;
    if (is_cpu_exclusive(cur) && !cpuset_cpumask_can_shrink(cur->cpus_allowed, trial->cpus_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 effective cpus_allowed masks?
 */
static int cpusets_overlap(struct cpuset *a, struct cpuset *b)
{
    return cpumask_intersects(a->effective_cpus, b->effective_cpus);
}

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) {
        /* 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();
}

/* Must be called with cpuset_mutex held.  */
static inline int nr_cpusets(void)
{
    /* jump label reference count + the top-level cpuset */
    return static_key_count(&cpusets_enabled_key.key) + 1;
}

/*
 * 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/admin-guide/cgroup-v1/cpusets.rst
 * 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:
 *    cp - cpuset pointer, used (together with pos_css) to perform a
 *       top-down scan of all cpusets. 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;               /* top-down scan of cpusets */
    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;
    bool root_load_balance = is_sched_load_balance(&top_cpuset);

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

    /* Special case for the 99% of systems with one, full, sched domain */
    if (root_load_balance && !top_cpuset.nr_subparts_cpus) {
        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_and(doms[0], top_cpuset.effective_cpus, housekeeping_cpumask(HK_FLAG_DOMAIN));

        goto done;
    }

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

    rcu_read_lock();
    if (root_load_balance) {
        csa[csn++] = &top_cpuset;
    }
    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 root is load-balancing, we can skip @cp if it
         * is a subset of the root's effective_cpus.
         */
        if (!cpumask_empty(cp->cpus_allowed) &&
            !(is_sched_load_balance(cp) &&
              cpumask_intersects(cp->cpus_allowed, housekeeping_cpumask(HK_FLAG_DOMAIN)))) {
            continue;
        }

        if (root_load_balance && cpumask_subset(cp->cpus_allowed, top_cpuset.effective_cpus)) {
            continue;
        }

        if (is_sched_load_balance(cp) && !cpumask_empty(cp->effective_cpus)) {
            csa[csn++] = cp;
        }

        /* skip @cp's subtree if not a partition root */
        if (!is_partition_root(cp)) {
            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_array(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->effective_cpus);
                cpumask_and(dp, dp, housekeeping_cpumask(HK_FLAG_DOMAIN));
                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;
}

static void update_tasks_root_domain(struct cpuset *cs)
{
    struct css_task_iter it;
    struct task_struct *task;

    css_task_iter_start(&cs->css, 0, &it);

    while ((task = css_task_iter_next(&it))) {
        dl_add_task_root_domain(task);
    }

    css_task_iter_end(&it);
}

static void rebuild_root_domains(void)
{
    struct cpuset *cs = NULL;
    struct cgroup_subsys_state *pos_css;

    lockdep_assert_held(&cpuset_mutex);
    lockdep_assert_cpus_held();
    lockdep_assert_held(&sched_domains_mutex);

    rcu_read_lock();

    /*
     * Clear default root domain DL accounting, it will be computed again
     * if a task belongs to it.
     */
    dl_clear_root_domain(&def_root_domain);

    cpuset_for_each_descendant_pre(cs, pos_css, &top_cpuset) {
        if (cpumask_empty(cs->effective_cpus)) {
            pos_css = css_rightmost_descendant(pos_css);
            continue;
        }

        css_get(&cs->css);

        rcu_read_unlock();

        update_tasks_root_domain(cs);

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

static void partition_and_rebuild_sched_domains(int ndoms_new, cpumask_var_t doms_new[],
                                                struct sched_domain_attr *dattr_new)
{
    mutex_lock(&sched_domains_mutex);
    partition_sched_domains_locked(ndoms_new, doms_new, dattr_new);
    rebuild_root_domains();
    mutex_unlock(&sched_domains_mutex);
}

/*
 * 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 cgroup_subsys_state *pos_css;
    struct sched_domain_attr *attr;
    cpumask_var_t *doms;
    struct cpuset *cs;
    int ndoms;

    lockdep_assert_held(&cpuset_mutex);

    /*
     * If we have raced with CPU hotplug, return early to avoid
     * passing doms with offlined cpu to partition_sched_domains().
     * Anyways, cpuset_hotplug_workfn() will rebuild sched domains.
     *
     * With no CPUs in any subpartitions, top_cpuset's effective CPUs
     * should be the same as the active CPUs, so checking only top_cpuset
     * is enough to detect racing CPU offlines.
     */
    if (!top_cpuset.nr_subparts_cpus && !cpumask_equal(top_cpuset.effective_cpus, cpu_active_mask)) {
        return;
    }

    /*
     * With subpartition CPUs, however, the effective CPUs of a partition
     * root should be only a subset of the active CPUs.  Since a CPU in any
     * partition root could be offlined, all must be checked.
     */
    if (top_cpuset.nr_subparts_cpus) {
        rcu_read_lock();
        cpuset_for_each_descendant_pre(cs, pos_css, &top_cpuset) {
            if (!is_partition_root(cs)) {
                pos_css = css_rightmost_descendant(pos_css);
                continue;
            }
            if (!cpumask_subset(cs->effective_cpus, cpu_active_mask)) {
                rcu_read_unlock();
                return;
            }
        }
        rcu_read_unlock();
    }

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

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

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

static int update_cpus_allowed(struct cpuset *cs, struct task_struct *p, const struct cpumask *new_mask)
{
    return set_cpus_allowed_ptr(p, new_mask);
}

/**
 * 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 css_task_iter it;
    struct task_struct *task;

    css_task_iter_start(&cs->css, 0, &it);
    while ((task = css_task_iter_next(&it))) {
        update_cpus_allowed(cs, task, cs->effective_cpus);
    }
    css_task_iter_end(&it);
}

/**
 * compute_effective_cpumask - Compute the effective cpumask of the cpuset
 * @new_cpus: the temp variable for the new effective_cpus mask
 * @cs: the cpuset the need to recompute the new effective_cpus mask
 * @parent: the parent cpuset
 *
 * If the parent has subpartition CPUs, include them in the list of
 * allowable CPUs in computing the new effective_cpus mask. Since offlined
 * CPUs are not removed from subparts_cpus, we have to use cpu_active_mask
 * to mask those out.
 */
static void compute_effective_cpumask(struct cpumask *new_cpus, struct cpuset *cs, struct cpuset *parent)
{
    if (parent->nr_subparts_cpus) {
        cpumask_or(new_cpus, parent->effective_cpus, parent->subparts_cpus);
        cpumask_and(new_cpus, new_cpus, cs->cpus_requested);
        cpumask_and(new_cpus, new_cpus, cpu_active_mask);
    } else {
        cpumask_and(new_cpus, cs->cpus_requested, parent_cs(cs)->effective_cpus);
    }
}

/*
 * Commands for update_parent_subparts_cpumask
 */
enum subparts_cmd {
    partcmd_enable,  /* Enable partition root     */
    partcmd_disable, /* Disable partition root     */
    partcmd_update,  /* Update parent's subparts_cpus */
};

/**
 * update_parent_subparts_cpumask - update subparts_cpus mask of parent cpuset
 * @cpuset:  The cpuset that requests change in partition root state
 * @cmd:     Partition root state change command
 * @newmask: Optional new cpumask for partcmd_update
 * @tmp:     Temporary addmask and delmask
 * Return:   0, 1 or an error code
 *
 * For partcmd_enable, the cpuset is being transformed from a non-partition
 * root to a partition root. The cpus_allowed mask of the given cpuset will
 * be put into parent's subparts_cpus and taken away from parent's
 * effective_cpus. The function will return 0 if all the CPUs listed in
 * cpus_allowed can be granted or an error code will be returned.
 *
 * For partcmd_disable, the cpuset is being transofrmed from a partition
 * root back to a non-partition root. Any CPUs in cpus_allowed that are in
 * parent's subparts_cpus will be taken away from that cpumask and put back
 * into parent's effective_cpus. 0 should always be returned.
 *
 * For partcmd_update, if the optional newmask is specified, the cpu
 * list is to be changed from cpus_allowed to newmask. Otherwise,
 * cpus_allowed is assumed to remain the same. The cpuset should either
 * be a partition root or an invalid partition root. The partition root
 * state may change if newmask is NULL and none of the requested CPUs can
 * be granted by the parent. The function will return 1 if changes to
 * parent's subparts_cpus and effective_cpus happen or 0 otherwise.
 * Error code should only be returned when newmask is non-NULL.
 *
 * The partcmd_enable and partcmd_disable commands are used by
 * update_prstate(). The partcmd_update command is used by
 * update_cpumasks_hier() with newmask NULL and update_cpumask() with
 * newmask set.
 *
 * The checking is more strict when enabling partition root than the
 * other two commands.
 *
 * Because of the implicit cpu exclusive nature of a partition root,
 * cpumask changes that violates the cpu exclusivity rule will not be
 * permitted when checked by validate_change(). The validate_change()
 * function will also prevent any changes to the cpu list if it is not
 * a superset of children's cpu lists.
 */
static int update_parent_subparts_cpumask(struct cpuset *cpuset, int cmd, struct cpumask *newmask, struct tmpmasks *tmp)
{
    struct cpuset *parent = parent_cs(cpuset);
    int adding;   /* Moving cpus from effective_cpus to subparts_cpus */
    int deleting; /* Moving cpus from subparts_cpus to effective_cpus */
    int new_prs;
    bool part_error = false; /* Partition error? */

    lockdep_assert_held(&cpuset_mutex);

    /*
     * The parent must be a partition root.
     * The new cpumask, if present, or the current cpus_allowed must
     * not be empty.
     */
    if (!is_partition_root(parent) || (newmask && cpumask_empty(newmask)) ||
        (!newmask && cpumask_empty(cpuset->cpus_allowed))) {
        return -EINVAL;
    }

    /*
     * Enabling/disabling partition root is not allowed if there are
     * online children.
     */
    if ((cmd != partcmd_update) && css_has_online_children(&cpuset->css)) {
        return -EBUSY;
    }

    /*
     * Enabling partition root is not allowed if not all the CPUs
     * can be granted from parent's effective_cpus or at least one
     * CPU will be left after that.
     */
    if ((cmd == partcmd_enable) && (!cpumask_subset(cpuset->cpus_allowed, parent->effective_cpus) ||
                                    cpumask_equal(cpuset->cpus_allowed, parent->effective_cpus))) {
        return -EINVAL;
    }

    /*
     * A cpumask update cannot make parent's effective_cpus become empty.
     */
    adding = deleting = false;
    new_prs = cpuset->partition_root_state;
    if (cmd == partcmd_enable) {
        cpumask_copy(tmp->addmask, cpuset->cpus_allowed);
        adding = true;
    } else if (cmd == partcmd_disable) {
        deleting = cpumask_and(tmp->delmask, cpuset->cpus_allowed, parent->subparts_cpus);
    } else if (newmask) {
        /*
         * partcmd_update with newmask:
         *
         * delmask = cpus_allowed & ~newmask & parent->subparts_cpus
         * addmask = newmask & parent->effective_cpus
         *             & ~parent->subparts_cpus
         */
        cpumask_andnot(tmp->delmask, cpuset->cpus_allowed, newmask);
        deleting = cpumask_and(tmp->delmask, tmp->delmask, parent->subparts_cpus);

        cpumask_and(tmp->addmask, newmask, parent->effective_cpus);
        adding = cpumask_andnot(tmp->addmask, tmp->addmask, parent->subparts_cpus);
        /*
         * Return error if the new effective_cpus could become empty.
         */
        if (adding && cpumask_equal(parent->effective_cpus, tmp->addmask)) {
            if (!deleting) {
                return -EINVAL;
            }
            /*
             * As some of the CPUs in subparts_cpus might have
             * been offlined, we need to compute the real delmask
             * to confirm that.
             */
            if (!cpumask_and(tmp->addmask, tmp->delmask, cpu_active_mask)) {
                return -EINVAL;
            }
            cpumask_copy(tmp->addmask, parent->effective_cpus);
        }
    } else {
        /*
         * partcmd_update w/o newmask:
         *
         * addmask = cpus_allowed & parent->effective_cpus
         *
         * Note that parent's subparts_cpus may have been
         * pre-shrunk in case there is a change in the cpu list.
         * So no deletion is needed.
         */
        adding = cpumask_and(tmp->addmask, cpuset->cpus_allowed, parent->effective_cpus);
        part_error = cpumask_equal(tmp->addmask, parent->effective_cpus);
    }

    if (cmd == partcmd_update) {
        int prev_prs = cpuset->partition_root_state;

        /*
         * Check for possible transition between PRS_ENABLED
         * and PRS_ERROR.
         */
        switch (cpuset->partition_root_state) {
            case PRS_ENABLED:
                if (part_error) {
                    new_prs = PRS_ERROR;
                }
                break;
            case PRS_ERROR:
                if (!part_error) {
                    new_prs = PRS_ENABLED;
                }
                break;
            default:
                break;
        }
        /*
         * Set part_error if previously in invalid state.
         */
        part_error = (prev_prs == PRS_ERROR);
    }

    if (!part_error && (new_prs == PRS_ERROR)) {
        return 0; /* Nothing need to be done */
    }

    if (new_prs == PRS_ERROR) {
        /*
         * Remove all its cpus from parent's subparts_cpus.
         */
        adding = false;
        deleting = cpumask_and(tmp->delmask, cpuset->cpus_allowed, parent->subparts_cpus);
    }

    if (!adding && !deleting && (new_prs == cpuset->partition_root_state)) {
        return 0;
    }

    /*
     * Change the parent's subparts_cpus.
     * Newly added CPUs will be removed from effective_cpus and
     * newly deleted ones will be added back to effective_cpus.
     */
    spin_lock_irq(&callback_lock);
    if (adding) {
        cpumask_or(parent->subparts_cpus, parent->subparts_cpus, tmp->addmask);
        cpumask_andnot(parent->effective_cpus, parent->effective_cpus, tmp->addmask);
    }
    if (deleting) {
        cpumask_andnot(parent->subparts_cpus, parent->subparts_cpus, tmp->delmask);
        /*
         * Some of the CPUs in subparts_cpus might have been offlined.
         */
        cpumask_and(tmp->delmask, tmp->delmask, cpu_active_mask);
        cpumask_or(parent->effective_cpus, parent->effective_cpus, tmp->delmask);
    }

    parent->nr_subparts_cpus = cpumask_weight(parent->subparts_cpus);

    if (cpuset->partition_root_state != new_prs) {
        cpuset->partition_root_state = new_prs;
    }
    spin_unlock_irq(&callback_lock);

    return cmd == partcmd_update;
}

/*
 * update_cpumasks_hier - Update effective cpumasks and tasks in the subtree
 * @cs:  the cpuset to consider
 * @tmp: temp variables for calculating effective_cpus & partition setup
 *
 * 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 tmpmasks *tmp)
{
    struct cpuset *cp;
    struct cgroup_subsys_state *pos_css;
    bool need_rebuild_sched_domains = false;
    int new_prs;

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

        compute_effective_cpumask(tmp->new_cpus, cp, parent);

        /*
         * If it becomes empty, inherit the effective mask of the
         * parent, which is guaranteed to have some CPUs.
         */
        if (is_in_v2_mode() && cpumask_empty(tmp->new_cpus)) {
            cpumask_copy(tmp->new_cpus, parent->effective_cpus);
            if (!cp->use_parent_ecpus) {
                cp->use_parent_ecpus = true;
                parent->child_ecpus_count++;
            }
        } else if (cp->use_parent_ecpus) {
            cp->use_parent_ecpus = false;
            WARN_ON_ONCE(!parent->child_ecpus_count);
            parent->child_ecpus_count--;
        }

        /*
         * Skip the whole subtree if the cpumask remains the same
         * and has no partition root state.
         */
        if (!cp->partition_root_state && cpumask_equal(tmp->new_cpus, cp->effective_cpus)) {
            pos_css = css_rightmost_descendant(pos_css);
            continue;
        }

        /*
         * update_parent_subparts_cpumask() should have been called
         * for cs already in update_cpumask(). We should also call
         * update_tasks_cpumask() again for tasks in the parent
         * cpuset if the parent's subparts_cpus changes.
         */
        new_prs = cp->partition_root_state;
        if ((cp != cs) && new_prs) {
            switch (parent->partition_root_state) {
                case PRS_DISABLED:
                    /*
                     * If parent is not a partition root or an
                     * invalid partition root, clear its state
                     * and its CS_CPU_EXCLUSIVE flag.
                     */
                    WARN_ON_ONCE(cp->partition_root_state != PRS_ERROR);
                    new_prs = PRS_DISABLED;

                    /*
                     * clear_bit() is an atomic operation and
                     * readers aren't interested in the state
                     * of CS_CPU_EXCLUSIVE anyway. So we can
                     * just update the flag without holding
                     * the callback_lock.
                     */
                    clear_bit(CS_CPU_EXCLUSIVE, &cp->flags);
                    break;

                case PRS_ENABLED:
                    if (update_parent_subparts_cpumask(cp, partcmd_update, NULL, tmp)) {
                        update_tasks_cpumask(parent);
                    }
                    break;

                case PRS_ERROR:
                    /*
                     * When parent is invalid, it has to be too.
                     */
                    new_prs = PRS_ERROR;
                    break;
            }
        }

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

        spin_lock_irq(&callback_lock);

        cpumask_copy(cp->effective_cpus, tmp->new_cpus);
        if (cp->nr_subparts_cpus && (new_prs != PRS_ENABLED)) {
            cp->nr_subparts_cpus = 0;
            cpumask_clear(cp->subparts_cpus);
        } else if (cp->nr_subparts_cpus) {
            /*
             * Make sure that effective_cpus & subparts_cpus
             * are mutually exclusive.
             *
             * In the unlikely event that effective_cpus
             * becomes empty. we clear cp->nr_subparts_cpus and
             * let its child partition roots to compete for
             * CPUs again.
             */
            cpumask_andnot(cp->effective_cpus, cp->effective_cpus, cp->subparts_cpus);
            if (cpumask_empty(cp->effective_cpus)) {
                cpumask_copy(cp->effective_cpus, tmp->new_cpus);
                cpumask_clear(cp->subparts_cpus);
                cp->nr_subparts_cpus = 0;
            } else if (!cpumask_subset(cp->subparts_cpus, tmp->new_cpus)) {
                cpumask_andnot(cp->subparts_cpus, cp->subparts_cpus, tmp->new_cpus);
                cp->nr_subparts_cpus = cpumask_weight(cp->subparts_cpus);
            }
        }

        if (new_prs != cp->partition_root_state) {
            cp->partition_root_state = new_prs;
        }

        spin_unlock_irq(&callback_lock);

        WARN_ON(!is_in_v2_mode() && !cpumask_equal(cp->cpus_allowed, cp->effective_cpus));

        update_tasks_cpumask(cp);

        /*
         * On legacy hierarchy, if the effective cpumask of any non-
         * empty cpuset is changed, we need to rebuild sched domains.
         * On default hierarchy, the cpuset needs to be a partition
         * root as well.
         */
        if (!cpumask_empty(cp->cpus_allowed) && is_sched_load_balance(cp) &&
            (!cgroup_subsys_on_dfl(cpuset_cgrp_subsys) || is_partition_root(cp))) {
            need_rebuild_sched_domains = true;
        }

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

    if (need_rebuild_sched_domains) {
        rebuild_sched_domains_locked();
    }
}

/**
 * update_sibling_cpumasks - Update siblings cpumasks
 * @parent:  Parent cpuset
 * @cs:      Current cpuset
 * @tmp:     Temp variables
 */
static void update_sibling_cpumasks(struct cpuset *parent, struct cpuset *cs, struct tmpmasks *tmp)
{
    struct cpuset *sibling;
    struct cgroup_subsys_state *pos_css;

    percpu_rwsem_assert_held(&cpuset_rwsem);
    /*
     * Check all its siblings and call update_cpumasks_hier()
     * if their use_parent_ecpus flag is set in order for them
     * to use the right effective_cpus value.
     */
    rcu_read_lock();
    cpuset_for_each_child(sibling, pos_css, parent) {
        if (sibling == cs) {
            continue;
        }
        if (!sibling->use_parent_ecpus) {
            continue;
        }
        if (!css_tryget_online(&sibling->css)) {
            continue;
        }
        rcu_read_unlock();
        update_cpumasks_hier(sibling, tmp);
        rcu_read_lock();
        css_put(&sibling->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;
    struct tmpmasks tmp;

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

    /*
     * An empty cpus_requested 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_requested);
    } else {
        retval = cpulist_parse(buf, trialcs->cpus_requested);
        if (retval < 0) {
            return retval;
        }
    }

    if (!cpumask_subset(trialcs->cpus_requested, cpu_present_mask)) {
        return -EINVAL;
    }

    cpumask_and(trialcs->cpus_allowed, trialcs->cpus_requested, cpu_active_mask);

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

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

#ifdef CONFIG_CPUMASK_OFFSTACK
    /*
     * Use the cpumasks in trialcs for tmpmasks when they are pointers
     * to allocated cpumasks.
     */
    tmp.addmask = trialcs->subparts_cpus;
    tmp.delmask = trialcs->effective_cpus;
    tmp.new_cpus = trialcs->cpus_allowed;
#endif

    if (cs->partition_root_state) {
        /* Cpumask of a partition root cannot be empty */
        if (cpumask_empty(trialcs->cpus_allowed)) {
            return -EINVAL;
        }
        if (update_parent_subparts_cpumask(cs, partcmd_update, trialcs->cpus_allowed, &tmp) < 0) {
            return -EINVAL;
        }
    }

    spin_lock_irq(&callback_lock);
    cpumask_copy(cs->cpus_allowed, trialcs->cpus_allowed);
    cpumask_copy(cs->cpus_requested, trialcs->cpus_requested);

    /*
     * Make sure that subparts_cpus is a subset of cpus_allowed.
     */
    if (cs->nr_subparts_cpus) {
        cpumask_and(cs->subparts_cpus, cs->subparts_cpus, cs->cpus_allowed);
        cs->nr_subparts_cpus = cpumask_weight(cs->subparts_cpus);
    }
    spin_unlock_irq(&callback_lock);

    update_cpumasks_hier(cs, &tmp);

    if (cs->partition_root_state) {
        struct cpuset *parent = parent_cs(cs);

        /*
         * For partition root, update the cpumasks of sibling
         * cpusets if they use parent's effective_cpus.
         */
        if (parent->child_ecpus_count) {
            update_sibling_cpumasks(parent, cs, &tmp);
        }
    }
    return 0;
}

/*
 * Migrate memory region from one set of nodes to another.  This is
 * performed asynchronously as it can be called from process migration path
 * holding locks involved in process management.  All mm migrations are
 * performed in the queued order and can be waited for by flushing
 * cpuset_migrate_mm_wq.
 */

struct cpuset_migrate_mm_work {
    struct work_struct work;
    struct mm_struct *mm;
    nodemask_t from;
    nodemask_t to;
};

static void cpuset_migrate_mm_workfn(struct work_struct *work)
{
    struct cpuset_migrate_mm_work *mwork = container_of(work, struct cpuset_migrate_mm_work, work);

    /* on a wq worker, no need to worry about %current's mems_allowed */
    do_migrate_pages(mwork->mm, &mwork->from, &mwork->to, MPOL_MF_MOVE_ALL);
    mmput(mwork->mm);
    kfree(mwork);
}

static void cpuset_migrate_mm(struct mm_struct *mm, const nodemask_t *from, const nodemask_t *to)
{
    struct cpuset_migrate_mm_work *mwork;

    mwork = kzalloc(sizeof(*mwork), GFP_KERNEL);
    if (mwork) {
        mwork->mm = mm;
        mwork->from = *from;
        mwork->to = *to;
        INIT_WORK(&mwork->work, cpuset_migrate_mm_workfn);
        queue_work(cpuset_migrate_mm_wq, &mwork->work);
    } else {
        mmput(mm);
    }
}

static void cpuset_post_attach(void)
{
    flush_workqueue(cpuset_migrate_mm_wq);
}

/*
 * 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
 *
 * We use the mems_allowed_seq seqlock to safely update both tsk->mems_allowed
 * and rebind an eventual tasks' mempolicy. If the task is allocating in
 * parallel, it might temporarily see an empty intersection, which results in
 * a seqlock check and retry before OOM or allocation failure.
 */
static void cpuset_change_task_nodemask(struct task_struct *tsk, nodemask_t *newmems)
{
    task_lock(tsk);

    local_irq_disable();
    write_seqcount_begin(&tsk->mems_allowed_seq);

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

    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 css_task_iter it;
    struct task_struct *task;

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

    guarantee_online_mems(cs, &newmems);

    /*
     * The mpol_rebind_mm() call takes mmap_lock, 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, 0, &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);
        } else {
            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 (is_in_v2_mode() && 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();

        spin_lock_irq(&callback_lock);
        cp->effective_mems = *new_mems;
        spin_unlock_irq(&callback_lock);

        WARN_ON(!is_in_v2_mode() && !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_lock during call.
 * Will take tasklist_lock, scan tasklist for tasks in cpuset cs,
 * lock each such tasks mm->mmap_lock, 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, top_cpuset.mems_allowed)) {
            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;
    }

    spin_lock_irq(&callback_lock);
    cs->mems_allowed = trialcs->mems_allowed;
    spin_unlock_irq(&callback_lock);

    /* use trialcs->mems_allowed as a temp variable */
    update_nodemasks_hier(cs, &trialcs->mems_allowed);
done:
    return retval;
}

bool current_cpuset_is_being_rebound(void)
{
    bool ret;

    rcu_read_lock();
    ret = task_cs(current) == cpuset_being_rebound;
    rcu_read_unlock();

    return ret;
}

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, 0, &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)));

    spin_lock_irq(&callback_lock);
    cs->flags = trialcs->flags;
    spin_unlock_irq(&callback_lock);

    if (!cpumask_empty(trialcs->cpus_allowed) && balance_flag_changed) {
        rebuild_sched_domains_locked();
    }

    if (spread_flag_changed) {
        update_tasks_flags(cs);
    }
out:
    free_cpuset(trialcs);
    return err;
}

/*
 * update_prstate - update partititon_root_state
 * cs: the cpuset to update
 * new_prs: new partition root state
 *
 * Call with cpuset_mutex held.
 */
static int update_prstate(struct cpuset *cs, int new_prs)
{
    int err, old_prs = cs->partition_root_state;
    struct cpuset *parent = parent_cs(cs);
    struct tmpmasks tmpmask;

    if (old_prs == new_prs) {
        return 0;
    }

    /*
     * Cannot force a partial or invalid partition root to a full
     * partition root.
     */
    if (new_prs && (old_prs == PRS_ERROR)) {
        return -EINVAL;
    }

    if (alloc_cpumasks(NULL, &tmpmask)) {
        return -ENOMEM;
    }

    err = -EINVAL;
    if (!old_prs) {
        /*
         * Turning on partition root requires setting the
         * CS_CPU_EXCLUSIVE bit implicitly as well and cpus_allowed
         * cannot be NULL.
         */
        if (cpumask_empty(cs->cpus_allowed)) {
            goto out;
        }

        err = update_flag(CS_CPU_EXCLUSIVE, cs, 1);
        if (err) {
            goto out;
        }

        err = update_parent_subparts_cpumask(cs, partcmd_enable, NULL, &tmpmask);
        if (err) {
            update_flag(CS_CPU_EXCLUSIVE, cs, 0);
            goto out;
        }
    } else {
        /*
         * Turning off partition root will clear the
         * CS_CPU_EXCLUSIVE bit.
         */
        if (old_prs == PRS_ERROR) {
            update_flag(CS_CPU_EXCLUSIVE, cs, 0);
            err = 0;
            goto out;
        }

        err = update_parent_subparts_cpumask(cs, partcmd_disable, NULL, &tmpmask);
        if (err) {
            goto out;
        }

        /* Turning off CS_CPU_EXCLUSIVE will not return error */
        update_flag(CS_CPU_EXCLUSIVE, cs, 0);
    }

    /*
     * Update cpumask of parent's tasks except when it is the top
     * cpuset as some system daemons cannot be mapped to other CPUs.
     */
    if (parent != &top_cpuset) {
        update_tasks_cpumask(parent);
    }

    if (parent->child_ecpus_count) {
        update_sibling_cpumasks(parent, cs, &tmpmask);
    }

    rebuild_sched_domains_locked();
out:
    if (!err) {
        spin_lock_irq(&callback_lock);
        cs->partition_root_state = new_prs;
        spin_unlock_irq(&callback_lock);
    }

    free_cpumasks(NULL, &tmpmask);
    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 ((u32)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)
{
    time64_t now;
    u32 ticks;

    now = ktime_get_seconds();
    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_taskset *tset)
{
    struct cgroup_subsys_state *css;
    struct cpuset *cs;
    struct task_struct *task;
    int ret;

    /* used later by cpuset_attach() */
    cpuset_attach_old_cs = task_cs(cgroup_taskset_first(tset, &css));
    cs = css_cs(css);

    mutex_lock(&cpuset_mutex);

    /* allow moving tasks into an empty cpuset if on default hierarchy */
    ret = -ENOSPC;
    if (!is_in_v2_mode() && (cpumask_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed))) {
        goto out_unlock;
    }

    cgroup_taskset_for_each(task, css, tset)
    {
        ret = task_can_attach(task, cs->effective_cpus);
        if (ret) {
            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_taskset *tset)
{
    struct cgroup_subsys_state *css;

    cgroup_taskset_first(tset, &css);

    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_taskset *tset)
{
    /* static buf protected by cpuset_mutex */
    static nodemask_t cpuset_attach_nodemask_to;
    struct task_struct *task;
    struct task_struct *leader;
    struct cgroup_subsys_state *css;
    struct cpuset *cs;
    struct cpuset *oldcs = cpuset_attach_old_cs;

    cgroup_taskset_first(tset, &css);
    cs = css_cs(css);

    mutex_lock(&cpuset_mutex);

    guarantee_online_mems(cs, &cpuset_attach_nodemask_to);

    cgroup_taskset_for_each(task, css, tset)
    {
        if (cs != &top_cpuset) {
            guarantee_online_cpus(task, cpus_attach);
        } else {
            cpumask_copy(cpus_attach, task_cpu_possible_mask(task));
        }
        /*
         * can_attach beforehand should guarantee that this doesn't
         * fail. have a better way to handle failure here
         */
        WARN_ON_ONCE(update_cpus_allowed(cs, task, cpus_attach));

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

    /*
     * Change mm for all threadgroup leaders. This is expensive and may
     * sleep and should be moved outside migration path proper.
     */
    cpuset_attach_nodemask_to = cs->effective_mems;
    cgroup_taskset_for_each_leader(leader, css, tset)
    {
        struct mm_struct *mm = get_task_mm(leader);

        if (mm) {
            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, &oldcs->old_mems_allowed, &cpuset_attach_nodemask_to);
            } else {
                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_EFFECTIVE_CPULIST,
    FILE_EFFECTIVE_MEMLIST,
    FILE_SUBPARTS_CPULIST,
    FILE_CPU_EXCLUSIVE,
    FILE_MEM_EXCLUSIVE,
    FILE_MEM_HARDWALL,
    FILE_SCHED_LOAD_BALANCE,
    FILE_PARTITION_ROOT,
    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;

    get_online_cpus();
    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_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);
    put_online_cpus();
    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;

    get_online_cpus();
    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);
    put_online_cpus();
    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.
     *
     * cpuset_hotplug_work calls back into cgroup core via
     * cgroup_transfer_tasks() and waiting for it from a cgroupfs
     * operation like this one can lead to a deadlock through kernfs
     * active_ref protection.  Let's break the protection.  Losing the
     * protection is okay as we check whether @cs is online after
     * grabbing cpuset_mutex anyway.  This only happens on the legacy
     * hierarchies.
     */
    css_get(&cs->css);
    kernfs_break_active_protection(of->kn);
    flush_work(&cpuset_hotplug_work);

    get_online_cpus();
    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_cpuset(trialcs);
out_unlock:
    mutex_unlock(&cpuset_mutex);
    put_online_cpus();
    kernfs_unbreak_active_protection(of->kn);
    css_put(&cs->css);
    flush_workqueue(cpuset_migrate_mm_wq);
    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;
    int ret = 0;

    spin_lock_irq(&callback_lock);

    switch (type) {
        case FILE_CPULIST:
            seq_printf(sf, "%*pbl\n", cpumask_pr_args(cs->cpus_requested));
            break;
        case FILE_MEMLIST:
            seq_printf(sf, "%*pbl\n", nodemask_pr_args(&cs->mems_allowed));
            break;
        case FILE_EFFECTIVE_CPULIST:
            seq_printf(sf, "%*pbl\n", cpumask_pr_args(cs->effective_cpus));
            break;
        case FILE_EFFECTIVE_MEMLIST:
            seq_printf(sf, "%*pbl\n", nodemask_pr_args(&cs->effective_mems));
            break;
        case FILE_SUBPARTS_CPULIST:
            seq_printf(sf, "%*pbl\n", cpumask_pr_args(cs->subparts_cpus));
            break;
        default:
            ret = -EINVAL;
    }

    spin_unlock_irq(&callback_lock);
    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;
}

static int sched_partition_show(struct seq_file *seq, void *v)
{
    struct cpuset *cs = css_cs(seq_css(seq));

    switch (cs->partition_root_state) {
        case PRS_ENABLED:
            seq_puts(seq, "root\n");
            break;
        case PRS_DISABLED:
            seq_puts(seq, "member\n");
            break;
        case PRS_ERROR:
            seq_puts(seq, "root invalid\n");
            break;
        default:
            break;
    }
    return 0;
}

static ssize_t sched_partition_write(struct kernfs_open_file *of, char *buf, size_t nbytes, loff_t off)
{
    struct cpuset *cs = css_cs(of_css(of));
    int val;
    int retval = -ENODEV;

    buf = strstrip(buf);
    /*
     * Convert "root" to ENABLED, and convert "member" to DISABLED.
     */
    if (!strcmp(buf, "root")) {
        val = PRS_ENABLED;
    } else if (!strcmp(buf, "member")) {
        val = PRS_DISABLED;
    } else {
        return -EINVAL;
    }

    css_get(&cs->css);
    get_online_cpus();
    mutex_lock(&cpuset_mutex);
    if (!is_cpuset_online(cs)) {
        goto out_unlock;
    }

    retval = update_prstate(cs, val);
out_unlock:
    mutex_unlock(&cpuset_mutex);
    put_online_cpus();
    css_put(&cs->css);
    return retval ?: nbytes;
}

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

static struct cftype legacy_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 = "effective_cpus",
        .seq_show = cpuset_common_seq_show,
        .private = FILE_EFFECTIVE_CPULIST,
    },

    {
        .name = "effective_mems",
        .seq_show = cpuset_common_seq_show,
        .private = FILE_EFFECTIVE_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,
        .private = FILE_MEMORY_PRESSURE,
    },

    {
        .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 */
};

/*
 * This is currently a minimal set for the default hierarchy. It can be
 * expanded later on by migrating more features and control files from v1.
 */
static struct cftype dfl_files[] = {
    {
        .name = "cpus",
        .seq_show = cpuset_common_seq_show,
        .write = cpuset_write_resmask,
        .max_write_len = (100U + 6 * NR_CPUS),
        .private = FILE_CPULIST,
        .flags = CFTYPE_NOT_ON_ROOT,
    },

    {
        .name = "mems",
        .seq_show = cpuset_common_seq_show,
        .write = cpuset_write_resmask,
        .max_write_len = (100U + 6 * MAX_NUMNODES),
        .private = FILE_MEMLIST,
        .flags = CFTYPE_NOT_ON_ROOT,
    },

    {
        .name = "cpus.effective",
        .seq_show = cpuset_common_seq_show,
        .private = FILE_EFFECTIVE_CPULIST,
    },

    {
        .name = "mems.effective",
        .seq_show = cpuset_common_seq_show,
        .private = FILE_EFFECTIVE_MEMLIST,
    },

    {
        .name = "cpus.partition",
        .seq_show = sched_partition_show,
        .write = sched_partition_write,
        .private = FILE_PARTITION_ROOT,
        .flags = CFTYPE_NOT_ON_ROOT,
    },

    {
        .name = "cpus.subpartitions",
        .seq_show = cpuset_common_seq_show,
        .private = FILE_SUBPARTS_CPULIST,
        .flags = CFTYPE_DEBUG,
    },

    {} /* 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_cpumasks(cs, NULL)) {
        kfree(cs);
        return ERR_PTR(-ENOMEM);
    }

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

    return &cs->css;
}

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;
    }

    get_online_cpus();
    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();

    spin_lock_irq(&callback_lock);
    if (is_in_v2_mode()) {
        cpumask_copy(cs->effective_cpus, parent->effective_cpus);
        cs->effective_mems = parent->effective_mems;
        cs->use_parent_ecpus = true;
        parent->child_ecpus_count++;
    }
    spin_unlock_irq(&callback_lock);

    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();

    spin_lock_irq(&callback_lock);
    cs->mems_allowed = parent->mems_allowed;
    cs->effective_mems = parent->mems_allowed;
    cpumask_copy(cs->cpus_allowed, parent->cpus_allowed);
    cpumask_copy(cs->cpus_requested, parent->cpus_requested);
    cpumask_copy(cs->effective_cpus, parent->cpus_allowed);
    spin_unlock_irq(&callback_lock);
out_unlock:
    mutex_unlock(&cpuset_mutex);
    put_online_cpus();
    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(). That is not needed
 * in the default hierarchy where only changes in partition
 * will cause repartitioning.
 *
 * If the cpuset has the 'sched.partition' flag enabled, simulate
 * turning 'sched.partition" off.
 */

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

    get_online_cpus();
    mutex_lock(&cpuset_mutex);

    if (is_partition_root(cs)) {
        update_prstate(cs, 0);
    }

    if (!cgroup_subsys_on_dfl(cpuset_cgrp_subsys) && is_sched_load_balance(cs)) {
        update_flag(CS_SCHED_LOAD_BALANCE, cs, 0);
    }

    if (cs->use_parent_ecpus) {
        struct cpuset *parent = parent_cs(cs);

        cs->use_parent_ecpus = false;
        parent->child_ecpus_count--;
    }

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

    mutex_unlock(&cpuset_mutex);
    put_online_cpus();
}

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

    free_cpuset(cs);
}

static void cpuset_bind(struct cgroup_subsys_state *root_css)
{
    mutex_lock(&cpuset_mutex);
    spin_lock_irq(&callback_lock);

    if (is_in_v2_mode()) {
        cpumask_copy(top_cpuset.cpus_allowed, cpu_possible_mask);
        top_cpuset.mems_allowed = node_possible_map;
    } else {
        cpumask_copy(top_cpuset.cpus_allowed, top_cpuset.effective_cpus);
        top_cpuset.mems_allowed = top_cpuset.effective_mems;
    }

    spin_unlock_irq(&callback_lock);
    mutex_unlock(&cpuset_mutex);
}

/*
 * Make sure the new task conform to the current state of its parent,
 * which could have been changed by cpuset just after it inherits the
 * state from the parent and before it sits on the cgroup's task list.
 */
static void cpuset_fork(struct task_struct *task)
{
    int inherit_cpus = 0;
    if (task_css_is_root(task, cpuset_cgrp_id)) {
        return;
    }

    task->mems_allowed = current->mems_allowed;
}

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,
    .post_attach = cpuset_post_attach,
    .bind = cpuset_bind,
    .fork = cpuset_fork,
    .legacy_cftypes = legacy_files,
    .dfl_cftypes = dfl_files,
    .early_init = true,
    .threaded = true,
};

/**
 * cpuset_init - initialize cpusets at system boot
 *
 * Description: Initialize top_cpuset
 **/

int __init cpuset_init(void)
{
    BUG_ON(!alloc_cpumask_var(&top_cpuset.cpus_allowed, GFP_KERNEL));
    BUG_ON(!alloc_cpumask_var(&top_cpuset.cpus_requested, GFP_KERNEL));
    BUG_ON(!alloc_cpumask_var(&top_cpuset.effective_cpus, GFP_KERNEL));
    BUG_ON(!zalloc_cpumask_var(&top_cpuset.subparts_cpus, GFP_KERNEL));

    cpumask_setall(top_cpuset.cpus_allowed);
    cpumask_setall(top_cpuset.cpus_requested);
    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;

    BUG_ON(!alloc_cpumask_var(&cpus_attach, GFP_KERNEL));

    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");
    }
}

static void hotplug_update_tasks_legacy(struct cpuset *cs, struct cpumask *new_cpus, nodemask_t *new_mems,
                                        bool cpus_updated, bool mems_updated)
{
    bool is_empty;

    spin_lock_irq(&callback_lock);
    cpumask_copy(cs->cpus_allowed, new_cpus);
    cpumask_copy(cs->effective_cpus, new_cpus);
    cs->mems_allowed = *new_mems;
    cs->effective_mems = *new_mems;
    spin_unlock_irq(&callback_lock);

    /*
     * Don't call update_tasks_cpumask() if the cpuset becomes empty,
     * as the tasks will be migratecd to an ancestor.
     */
    if (cpus_updated && !cpumask_empty(cs->cpus_allowed)) {
        update_tasks_cpumask(cs);
    }
    if (mems_updated && !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);

    /*
     * 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 (is_empty) {
        remove_tasks_in_empty_cpuset(cs);
    }

    mutex_lock(&cpuset_mutex);
}

static void hotplug_update_tasks(struct cpuset *cs, struct cpumask *new_cpus, nodemask_t *new_mems, bool cpus_updated,
                                 bool mems_updated)
{
    if (cpumask_empty(new_cpus)) {
        cpumask_copy(new_cpus, parent_cs(cs)->effective_cpus);
    }
    if (nodes_empty(*new_mems)) {
        *new_mems = parent_cs(cs)->effective_mems;
    }

    spin_lock_irq(&callback_lock);
    cpumask_copy(cs->effective_cpus, new_cpus);
    cs->effective_mems = *new_mems;
    spin_unlock_irq(&callback_lock);

    if (cpus_updated) {
        update_tasks_cpumask(cs);
    }
    if (mems_updated) {
        update_tasks_nodemask(cs);
    }
}

static bool force_rebuild;

void cpuset_force_rebuild(void)
{
    force_rebuild = true;
}

/**
 * cpuset_hotplug_update_tasks - update tasks in a cpuset for hotunplug
 * @cs: cpuset in interest
 * @tmp: the tmpmasks structure pointer
 *
 * 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, struct tmpmasks *tmp)
{
    static cpumask_t new_cpus;
    static nodemask_t new_mems;
    bool cpus_updated;
    bool mems_updated;
    struct cpuset *parent;

    while (1) {
        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);
            continue;
        }
        break;
    }

    parent = parent_cs(cs);
    compute_effective_cpumask(&new_cpus, cs, parent);
    nodes_and(new_mems, cs->mems_allowed, parent->effective_mems);

    if (cs->nr_subparts_cpus) {
        /*
         * Make sure that CPUs allocated to child partitions
         * do not show up in effective_cpus.
         */
        cpumask_andnot(&new_cpus, &new_cpus, cs->subparts_cpus);
    }

    if (!tmp || !cs->partition_root_state) {
        goto update_tasks;
    }

    /*
     * In the unlikely event that a partition root has empty
     * effective_cpus or its parent becomes erroneous, we have to
     * transition it to the erroneous state.
     */
    if (is_partition_root(cs) && (cpumask_empty(&new_cpus) || (parent->partition_root_state == PRS_ERROR))) {
        if (cs->nr_subparts_cpus) {
            spin_lock_irq(&callback_lock);
            cs->nr_subparts_cpus = 0;
            cpumask_clear(cs->subparts_cpus);
            spin_unlock_irq(&callback_lock);
            compute_effective_cpumask(&new_cpus, cs, parent);
        }

        /*
         * If the effective_cpus is empty because the child
         * partitions take away all the CPUs, we can keep
         * the current partition and let the child partitions
         * fight for available CPUs.
         */
        if ((parent->partition_root_state == PRS_ERROR) || cpumask_empty(&new_cpus)) {
            update_parent_subparts_cpumask(cs, partcmd_disable, NULL, tmp);
            spin_lock_irq(&callback_lock);
            cs->partition_root_state = PRS_ERROR;
            spin_unlock_irq(&callback_lock);
        }
        cpuset_force_rebuild();
    }

    /*
     * On the other hand, an erroneous partition root may be transitioned
     * back to a regular one or a partition root with no CPU allocated
     * from the parent may change to erroneous.
     */
    if (is_partition_root(parent) &&
        ((cs->partition_root_state == PRS_ERROR) || !cpumask_intersects(&new_cpus, parent->subparts_cpus)) &&
        update_parent_subparts_cpumask(cs, partcmd_update, NULL, tmp)) {
        cpuset_force_rebuild();
    }

update_tasks:
    cpus_updated = !cpumask_equal(&new_cpus, cs->effective_cpus);
    mems_updated = !nodes_equal(new_mems, cs->effective_mems);

    if (is_in_v2_mode()) {
        hotplug_update_tasks(cs, &new_cpus, &new_mems, cpus_updated, mems_updated);
    } else {
        hotplug_update_tasks_legacy(cs, &new_cpus, &new_mems, cpus_updated, mems_updated);
    }

    mutex_unlock(&cpuset_mutex);
}

/**
 * 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.
 */
void cpuset_hotplug_workfn(struct work_struct *work)
{
    static cpumask_t new_cpus;
    static nodemask_t new_mems;
    bool cpus_updated, mems_updated;
    bool on_dfl = is_in_v2_mode();
    struct tmpmasks tmp, *ptmp = NULL;

    if (on_dfl && !alloc_cpumasks(NULL, &tmp)) {
        ptmp = &tmp;
    }

    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];

    /*
     * If subparts_cpus is populated, it is likely that the check below
     * will produce a false positive on cpus_updated when the cpu list
     * isn't changed. It is extra work, but it is better to be safe.
     */
    cpus_updated = !cpumask_equal(top_cpuset.effective_cpus, &new_cpus);
    mems_updated = !nodes_equal(top_cpuset.effective_mems, new_mems);

    /*
     * In the rare case that hotplug removes all the cpus in subparts_cpus,
     * we assumed that cpus are updated.
     */
    if (!cpus_updated && top_cpuset.nr_subparts_cpus) {
        cpus_updated = true;
    }

    /* synchronize cpus_allowed to cpu_active_mask */
    if (cpus_updated) {
        spin_lock_irq(&callback_lock);
        if (!on_dfl) {
            cpumask_copy(top_cpuset.cpus_allowed, &new_cpus);
        }
        /*
         * Make sure that CPUs allocated to child partitions
         * do not show up in effective_cpus. If no CPU is left,
         * we clear the subparts_cpus & let the child partitions
         * fight for the CPUs again.
         */
        if (top_cpuset.nr_subparts_cpus) {
            if (cpumask_subset(&new_cpus, top_cpuset.subparts_cpus)) {
                top_cpuset.nr_subparts_cpus = 0;
                cpumask_clear(top_cpuset.subparts_cpus);
            } else {
                cpumask_andnot(&new_cpus, &new_cpus, top_cpuset.subparts_cpus);
            }
        }
        cpumask_copy(top_cpuset.effective_cpus, &new_cpus);
        spin_unlock_irq(&callback_lock);
        /* we don't mess with cpumasks of tasks in top_cpuset */
    }

    /* synchronize mems_allowed to N_MEMORY */
    if (mems_updated) {
        spin_lock_irq(&callback_lock);
        if (!on_dfl) {
            top_cpuset.mems_allowed = new_mems;
        }
        top_cpuset.effective_mems = new_mems;
        spin_unlock_irq(&callback_lock);
        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, ptmp);

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

    /* rebuild sched domains if cpus_allowed has changed */
    if (cpus_updated || force_rebuild) {
        force_rebuild = false;
        rebuild_sched_domains();
    }

    free_cpumasks(NULL, ptmp);
}

void cpuset_update_active_cpus(void)
{
    /*
     * 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.
     */
    schedule_work(&cpuset_hotplug_work);
}

void cpuset_wait_for_hotplug(void)
{
    flush_work(&cpuset_hotplug_work);
}
EXPORT_SYMBOL_GPL(cpuset_wait_for_hotplug);

/*
 * 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)
{
   	/*
	 * cpus_allowd/mems_allowed set to v2 values in the initial
	 * cpuset_bind() call will be reset to v1 values in another
	 * cpuset_bind() call when v1 cpuset is mounted.
	 */
    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_migrate_mm_wq = alloc_ordered_workqueue("cpuset_migrate_mm", 0);
    BUG_ON(!cpuset_migrate_mm_wq);
}

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

void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
{
    unsigned long flags;

    spin_lock_irqsave(&callback_lock, flags);
    rcu_read_lock();
    guarantee_online_cpus(tsk, pmask);
    rcu_read_unlock();
    spin_unlock_irqrestore(&callback_lock, flags);
}
EXPORT_SYMBOL_GPL(cpuset_cpus_allowed);
/**
 * cpuset_cpus_allowed_fallback - final fallback before complete catastrophe.
 * @tsk: pointer to task_struct with which the scheduler is struggling
 *
 * Description: In the case that the scheduler cannot find an allowed cpu in
 * tsk->cpus_allowed, we fall back to task_cs(tsk)->cpus_allowed. In legacy
 * mode however, this value is the same as task_cs(tsk)->effective_cpus,
 * which will not contain a sane cpumask during cases such as cpu hotplugging.
 * This is the absolute last resort for the scheduler and it is only used if
 * _every_ other avenue has been traveled.
 **/

void cpuset_cpus_allowed_fallback(struct task_struct *tsk)
{
    const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);
    const struct cpumask *cs_mask;

    rcu_read_lock();
    cs_mask = task_cs(tsk)->cpus_allowed;
    if (!is_in_v2_mode() || !cpumask_subset(cs_mask, possible_mask)) {
        goto unlock; /* select_fallback_rq will try harder */
    }

    do_set_cpus_allowed(tsk, cs_mask);
unlock:
    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 __init 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)
{
    nodemask_t mask;
    unsigned long flags;

    spin_lock_irqsave(&callback_lock, flags);
    rcu_read_lock();
    guarantee_online_mems(task_cs(tsk), &mask);
    rcu_read_unlock();
    spin_unlock_irqrestore(&callback_lock, flags);

    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_lock.  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 - 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 @node is set in
 * current's mems_allowed, yes.  If it's not a __GFP_HARDWALL request and this
 * node is set in the nearest hardwalled cpuset ancestor to current's cpuset,
 * yes.  If current has access to memory reserves as an oom victim, yes.
 * Otherwise, no.
 *
 * 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.
 * GFP_KERNEL allocations are not so marked, so can escape to the
 * nearest enclosing hardwalled ancestor cpuset.
 *
 * Scanning up parent cpusets requires callback_lock.  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_lock.
 *
 * 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
 *    tsk_is_oom_victim   - any node ok
 *    GFP_KERNEL   - any node in enclosing hardwalled cpuset ok
 *    GFP_USER     - only nodes in current tasks mems allowed ok.
 */
bool _cpuset_node_allowed(int node, gfp_t gfp_mask)
{
    struct cpuset *cs; /* current cpuset ancestors */
    int allowed;       /* is allocation in zone z allowed? */
    unsigned long flags;

    if (in_interrupt()) {
        return true;
    }
    if (node_isset(node, current->mems_allowed)) {
        return true;
    }
    /*
     * Allow tasks that have access to memory reserves because they have
     * been OOM killed to get memory anywhere.
     */
    if (unlikely(tsk_is_oom_victim(current))) {
        return true;
    }
    if (gfp_mask & __GFP_HARDWALL) { /* If hardwall request, stop here */
        return false;
    }

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

    /* Not hardwall and node outside mems_allowed: scan up cpusets */
    spin_lock_irqsave(&callback_lock, flags);

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

    spin_unlock_irqrestore(&callback_lock, flags);
    return allowed;
}

/**
 * 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)
{
    return *rotor = next_node_in(*rotor, current->mems_allowed);
}

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);
}

/**
 * cpuset_print_current_mems_allowed - prints current's cpuset and mems_allowed
 *
 * Description: Prints current's name, cpuset name, and cached copy of its
 * mems_allowed to the kernel log.
 */
void cpuset_print_current_mems_allowed(void)
{
    struct cgroup *cgrp;

    rcu_read_lock();

    cgrp = task_cs(current)->css.cgroup;
    pr_cont(",cpuset=");
    pr_cont_cgroup_name(cgrp);
    pr_cont(",mems_allowed=%*pbl", nodemask_pr_args(&current->mems_allowed));

    rcu_read_unlock();
}

/*
 * 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, struct pid_namespace *ns, struct pid *pid, struct task_struct *tsk)
{
    char *buf;
    struct cgroup_subsys_state *css;
    int retval;

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

    css = task_get_css(tsk, cpuset_cgrp_id);
    retval = cgroup_path_ns(css->cgroup, buf, PATH_MAX, current->nsproxy->cgroup_ns);
    css_put(css);
    if (retval >= PATH_MAX) {
        retval = -ENAMETOOLONG;
    }
    if (retval < 0) {
        goto out_free;
    }
    seq_puts(m, buf);
    seq_putc(m, '\n');
    retval = 0;
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_printf(m, "Mems_allowed:\t%*pb\n", nodemask_pr_args(&task->mems_allowed));
    seq_printf(m, "Mems_allowed_list:\t%*pbl\n", nodemask_pr_args(&task->mems_allowed));
}