cpuset.c 74.6 KB
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/*
 *  kernel/cpuset.c
 *
 *  Processor and Memory placement constraints for sets of tasks.
 *
 *  Copyright (C) 2003 BULL SA.
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 *  Copyright (C) 2004-2007 Silicon Graphics, Inc.
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 *  Copyright (C) 2006 Google, Inc
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 *
 *  Portions derived from Patrick Mochel's sysfs code.
 *  sysfs is Copyright (c) 2001-3 Patrick Mochel
 *
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 *  2003-10-10 Written by Simon Derr.
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 *  2003-10-22 Updates by Stephen Hemminger.
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 *  2004 May-July Rework by Paul Jackson.
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 *  2006 Rework by Paul Menage to use generic cgroups
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 *  2008 Rework of the scheduler domains and CPU hotplug handling
 *       by Max Krasnyansky
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 *
 *  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>
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#include <linux/mempolicy.h>
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#include <linux/mm.h>
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#include <linux/memory.h>
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#include <linux/export.h>
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#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/pagemap.h>
#include <linux/proc_fs.h>
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#include <linux/rcupdate.h>
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#include <linux/sched.h>
#include <linux/seq_file.h>
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#include <linux/security.h>
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#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/stat.h>
#include <linux/string.h>
#include <linux/time.h>
#include <linux/backing-dev.h>
#include <linux/sort.h>

#include <asm/uaccess.h>
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#include <linux/atomic.h>
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#include <linux/mutex.h>
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#include <linux/workqueue.h>
#include <linux/cgroup.h>
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#include <linux/wait.h>
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/*
 * Tracks how many cpusets are currently defined in system.
 * When there is only one cpuset (the root cpuset) we can
 * short circuit some hooks.
 */
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int number_of_cpusets __read_mostly;
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/* See "Frequency meter" comments, below. */

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

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struct cpuset {
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	struct cgroup_subsys_state css;

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

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	/*
	 * 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;

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

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	/* partition number for rebuild_sched_domains() */
	int pn;
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	/* for custom sched domain */
	int relax_domain_level;
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};

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

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

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

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


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

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

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

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

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

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

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

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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);
}

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

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/**
 * cpuset_for_each_child - traverse online children of a cpuset
 * @child_cs: loop cursor pointing to the current child
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 * @pos_css: used for iteration
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 * @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.
 */
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#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)))))
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/**
 * cpuset_for_each_descendant_pre - pre-order walk of a cpuset's descendants
 * @des_cs: loop cursor pointing to the current descendant
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 * @pos_css: used for iteration
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 * @root_cs: target cpuset to walk ancestor of
 *
 * Walk @des_cs through the online descendants of @root_cs.  Must be used
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 * with RCU read locked.  The caller may modify @pos_css by calling
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 * css_rightmost_descendant() to skip subtree.  @root_cs is included in the
 * iteration and the first node to be visited.
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 */
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#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)))))
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/*
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 * There are two global mutexes guarding cpuset structures - cpuset_mutex
 * and callback_mutex.  The latter may nest inside the former.  We also
 * require taking task_lock() when dereferencing a task's cpuset pointer.
 * See "The task_lock() exception", at the end of this comment.
 *
 * A task must hold both mutexes to modify cpusets.  If a task holds
 * cpuset_mutex, then it blocks others wanting that mutex, ensuring that it
 * is the only task able to also acquire callback_mutex and be able to
 * modify cpusets.  It can perform various checks on the cpuset structure
 * first, knowing nothing will change.  It can also allocate memory while
 * just holding cpuset_mutex.  While it is performing these checks, various
 * callback routines can briefly acquire callback_mutex to query cpusets.
 * Once it is ready to make the changes, it takes callback_mutex, blocking
 * everyone else.
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 *
 * Calls to the kernel memory allocator can not be made while holding
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 * callback_mutex, as that would risk double tripping on callback_mutex
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 * from one of the callbacks into the cpuset code from within
 * __alloc_pages().
 *
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 * If a task is only holding callback_mutex, then it has read-only
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 * access to cpusets.
 *
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 * 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.
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 *
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 * The cpuset_common_file_read() handlers only hold callback_mutex across
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 * small pieces of code, such as when reading out possibly multi-word
 * cpumasks and nodemasks.
 *
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 * Accessing a task's cpuset should be done in accordance with the
 * guidelines for accessing subsystem state in kernel/cgroup.c
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 */

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

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static DECLARE_WAIT_QUEUE_HEAD(cpuset_attach_wq);

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

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

/*
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 * Return in pmask the portion of a cpusets's cpus_allowed that
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 * are online.  If none are online, walk up the cpuset hierarchy
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 * until we find one that does have some online cpus.  The top
 * cpuset always has some cpus online.
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 *
 * One way or another, we guarantee to return some non-empty subset
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 * of cpu_online_mask.
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 *
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 * Call with callback_mutex held.
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 */
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static void guarantee_online_cpus(struct cpuset *cs, struct cpumask *pmask)
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{
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	while (!cpumask_intersects(cs->cpus_allowed, cpu_online_mask))
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		cs = parent_cs(cs);
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	cpumask_and(pmask, cs->cpus_allowed, cpu_online_mask);
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}

/*
 * Return in *pmask the portion of a cpusets's mems_allowed that
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 * are online, with memory.  If none are online with memory, walk
 * up the cpuset hierarchy until we find one that does have some
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 * online mems.  The top cpuset always has some mems online.
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 *
 * One way or another, we guarantee to return some non-empty subset
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 * of node_states[N_MEMORY].
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 *
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 * Call with callback_mutex held.
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 */
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static void guarantee_online_mems(struct cpuset *cs, nodemask_t *pmask)
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{
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	while (!nodes_intersects(cs->mems_allowed, node_states[N_MEMORY]))
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		cs = parent_cs(cs);
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	nodes_and(*pmask, cs->mems_allowed, node_states[N_MEMORY]);
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}

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

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/*
 * 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
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 * are only set if the other's are set.  Call holding cpuset_mutex.
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 */

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

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

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

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

	return trial;
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}

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

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/*
 * 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
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 * cpuset_mutex held.
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 *
 * '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.
 */

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static int validate_change(struct cpuset *cur, struct cpuset *trial)
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{
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	struct cgroup_subsys_state *css;
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	struct cpuset *c, *par;
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	int ret;

	rcu_read_lock();
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	/* Each of our child cpusets must be a subset of us */
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	ret = -EBUSY;
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	cpuset_for_each_child(c, css, cur)
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		if (!is_cpuset_subset(c, trial))
			goto out;
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	/* Remaining checks don't apply to root cpuset */
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	ret = 0;
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	if (cur == &top_cpuset)
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		goto out;
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	par = parent_cs(cur);
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	/* We must be a subset of our parent cpuset */
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	ret = -EACCES;
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	if (!is_cpuset_subset(trial, par))
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		goto out;
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	/*
	 * If either I or some sibling (!= me) is exclusive, we can't
	 * overlap
	 */
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	ret = -EINVAL;
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	cpuset_for_each_child(c, css, par) {
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		if ((is_cpu_exclusive(trial) || is_cpu_exclusive(c)) &&
		    c != cur &&
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		    cpumask_intersects(trial->cpus_allowed, c->cpus_allowed))
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			goto out;
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		if ((is_mem_exclusive(trial) || is_mem_exclusive(c)) &&
		    c != cur &&
		    nodes_intersects(trial->mems_allowed, c->mems_allowed))
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			goto out;
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	}

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	/*
	 * Cpusets with tasks - existing or newly being attached - can't
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	 * be changed to have empty cpus_allowed or mems_allowed.
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	 */
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	ret = -ENOSPC;
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	if ((cgroup_has_tasks(cur->css.cgroup) || cur->attach_in_progress)) {
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		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;
	}
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	ret = 0;
out:
	rcu_read_unlock();
	return ret;
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}

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

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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;
}

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static void update_domain_attr_tree(struct sched_domain_attr *dattr,
				    struct cpuset *root_cs)
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{
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	struct cpuset *cp;
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	struct cgroup_subsys_state *pos_css;
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	rcu_read_lock();
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	cpuset_for_each_descendant_pre(cp, pos_css, root_cs) {
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		if (cp == root_cs)
			continue;

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

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/*
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 * 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.
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 * The output of this function needs to be passed to kernel/sched/core.c
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 * partition_sched_domains() routine, which will rebuild the scheduler's
 * load balancing domains (sched domains) as specified by that partial
 * partition.
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 *
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 * See "What is sched_load_balance" in Documentation/cgroups/cpusets.txt
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 * 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.
 *
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 * Must be called with cpuset_mutex held.
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 *
 * The three key local variables below are:
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 *    q  - a linked-list queue of cpuset pointers, used to implement a
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 *	   top-down scan of all cpusets.  This scan loads a pointer
 *	   to each cpuset marked is_sched_load_balance into the
 *	   array 'csa'.  For our purposes, rebuilding the schedulers
 *	   sched domains, we can ignore !is_sched_load_balance cpusets.
 *  csa  - (for CpuSet Array) Array of pointers to all the cpusets
 *	   that need to be load balanced, for convenient iterative
 *	   access by the subsequent code that finds the best partition,
 *	   i.e the set of domains (subsets) of CPUs such that the
 *	   cpus_allowed of every cpuset marked is_sched_load_balance
 *	   is a subset of one of these domains, while there are as
 *	   many such domains as possible, each as small as possible.
 * doms  - Conversion of 'csa' to an array of cpumasks, for passing to
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 *	   the kernel/sched/core.c routine partition_sched_domains() in a
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 *	   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().
 */
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static int generate_sched_domains(cpumask_var_t **domains,
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			struct sched_domain_attr **attributes)
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{
	struct cpuset *cp;	/* scans q */
	struct cpuset **csa;	/* array of all cpuset ptrs */
	int csn;		/* how many cpuset ptrs in csa so far */
	int i, j, k;		/* indices for partition finding loops */
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	cpumask_var_t *doms;	/* resulting partition; i.e. sched domains */
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	struct sched_domain_attr *dattr;  /* attributes for custom domains */
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	int ndoms = 0;		/* number of sched domains in result */
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	int nslot;		/* next empty doms[] struct cpumask slot */
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	struct cgroup_subsys_state *pos_css;
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	doms = NULL;
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	dattr = NULL;
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	csa = NULL;
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	/* Special case for the 99% of systems with one, full, sched domain */
	if (is_sched_load_balance(&top_cpuset)) {
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		ndoms = 1;
		doms = alloc_sched_domains(ndoms);
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		if (!doms)
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			goto done;

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

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

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	rcu_read_lock();
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	cpuset_for_each_descendant_pre(cp, pos_css, &top_cpuset) {
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		if (cp == &top_cpuset)
			continue;
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		/*
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		 * 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.
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		 */
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		if (!cpumask_empty(cp->cpus_allowed) &&
		    !is_sched_load_balance(cp))
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			continue;
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		if (is_sched_load_balance(cp))
			csa[csn++] = cp;

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

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

	/*
	 * The rest of the code, including the scheduler, can deal with
	 * dattr==NULL case. No need to abort if alloc fails.
	 */
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	dattr = kmalloc(ndoms * sizeof(struct sched_domain_attr), GFP_KERNEL);
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	for (nslot = 0, i = 0; i < csn; i++) {
		struct cpuset *a = csa[i];
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		struct cpumask *dp;
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		int apn = a->pn;

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

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		dp = doms[nslot];
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		if (nslot == ndoms) {
			static int warnings = 10;
			if (warnings) {
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				pr_warn("rebuild_sched_domains confused: nslot %d, ndoms %d, csn %d, i %d, apn %d\n",
					nslot, ndoms, csn, i, apn);
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				warnings--;
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			}
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			continue;
		}
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		cpumask_clear(dp);
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		if (dattr)
			*(dattr + nslot) = SD_ATTR_INIT;
		for (j = i; j < csn; j++) {
			struct cpuset *b = csa[j];

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

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

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done:
	kfree(csa);

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

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

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

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

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

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

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

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

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

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/*
 * update_tasks_cpumask_hier - Update the cpumasks of tasks in the hierarchy.
 * @root_cs: the root cpuset of the hierarchy
 * @update_root: update root cpuset or not?
 *
 * This will update cpumasks of tasks in @root_cs and all other empty cpusets
 * which take on cpumask of @root_cs.
 *
 * Called with cpuset_mutex held
 */
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static void update_tasks_cpumask_hier(struct cpuset *root_cs, bool update_root)
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{
	struct cpuset *cp;
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	struct cgroup_subsys_state *pos_css;
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	rcu_read_lock();
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	cpuset_for_each_descendant_pre(cp, pos_css, root_cs) {
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		if (cp == root_cs) {
			if (!update_root)
				continue;
		} else {
			/* skip the whole subtree if @cp have some CPU */
			if (!cpumask_empty(cp->cpus_allowed)) {
				pos_css = css_rightmost_descendant(pos_css);
				continue;
			}
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		}
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		if (!css_tryget_online(&cp->css))
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			continue;
		rcu_read_unlock();

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

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/**
 * update_cpumask - update the cpus_allowed mask of a cpuset and all tasks in it
 * @cs: the cpuset to consider
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 * @trialcs: trial cpuset
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 * @buf: buffer of cpu numbers written to this cpuset
 */
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static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
			  const char *buf)
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{
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	int retval;
	int is_load_balanced;
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	/* top_cpuset.cpus_allowed tracks cpu_online_mask; it's read-only */
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	if (cs == &top_cpuset)
		return -EACCES;

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	/*
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	 * An empty cpus_allowed is ok only if the cpuset has no tasks.
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	 * Since cpulist_parse() fails on an empty mask, we special case
	 * that parsing.  The validate_change() call ensures that cpusets
	 * with tasks have cpus.
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	 */
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	if (!*buf) {
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		cpumask_clear(trialcs->cpus_allowed);
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	} else {
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		retval = cpulist_parse(buf, trialcs->cpus_allowed);
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		if (retval < 0)
			return retval;
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		if (!cpumask_subset(trialcs->cpus_allowed, cpu_active_mask))
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			return -EINVAL;
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	}
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	/* Nothing to do if the cpus didn't change */
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	if (cpumask_equal(cs->cpus_allowed, trialcs->cpus_allowed))
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		return 0;
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	retval = validate_change(cs, trialcs);
	if (retval < 0)
		return retval;

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	is_load_balanced = is_sched_load_balance(trialcs);
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	mutex_lock(&callback_mutex);
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	cpumask_copy(cs->cpus_allowed, trialcs->cpus_allowed);
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	mutex_unlock(&callback_mutex);
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	update_tasks_cpumask_hier(cs, true);
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	if (is_load_balanced)
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		rebuild_sched_domains_locked();
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	return 0;
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}

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/*
 * cpuset_migrate_mm
 *
 *    Migrate memory region from one set of nodes to another.
 *
 *    Temporarilly set tasks mems_allowed to target nodes of migration,
 *    so that the migration code can allocate pages on these nodes.
 *
 *    While the mm_struct we are migrating is typically from some
 *    other task, the task_struct mems_allowed that we are hacking
 *    is for our current task, which must allocate new pages for that
 *    migrating memory region.
 */

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

	do_migrate_pages(mm, from, to, MPOL_MF_MOVE_ALL);

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

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/*
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 * cpuset_change_task_nodemask - change task's mems_allowed and mempolicy
 * @tsk: the task to change
 * @newmems: new nodes that the task will be set
 *
 * In order to avoid seeing no nodes if the old and new nodes are disjoint,
 * we structure updates as setting all new allowed nodes, then clearing newly
 * disallowed ones.
 */
static void cpuset_change_task_nodemask(struct task_struct *tsk,
					nodemask_t *newmems)
{
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	bool need_loop;
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	/*
	 * Allow tasks that have access to memory reserves because they have
	 * been OOM killed to get memory anywhere.
	 */
	if (unlikely(test_thread_flag(TIF_MEMDIE)))
		return;
	if (current->flags & PF_EXITING) /* Let dying task have memory */
		return;

	task_lock(tsk);
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	/*
	 * Determine if a loop is necessary if another thread is doing
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	 * read_mems_allowed_begin().  If at least one node remains unchanged and
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	 * tsk does not have a mempolicy, then an empty nodemask will not be
	 * possible when mems_allowed is larger than a word.
	 */
	need_loop = task_has_mempolicy(tsk) ||
			!nodes_intersects(*newmems, tsk->mems_allowed);
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	if (need_loop) {
		local_irq_disable();
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		write_seqcount_begin(&tsk->mems_allowed_seq);
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	}
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	nodes_or(tsk->mems_allowed, tsk->mems_allowed, *newmems);
	mpol_rebind_task(tsk, newmems, MPOL_REBIND_STEP1);
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	mpol_rebind_task(tsk, newmems, MPOL_REBIND_STEP2);
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	tsk->mems_allowed = *newmems;
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	if (need_loop) {
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		write_seqcount_end(&tsk->mems_allowed_seq);
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		local_irq_enable();
	}
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	task_unlock(tsk);
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}

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static void *cpuset_being_rebound;

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/**
 * 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
 *
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 * 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.
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 */
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static void update_tasks_nodemask(struct cpuset *cs)
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{
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	static nodemask_t newmems;	/* protected by cpuset_mutex */
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	struct cpuset *mems_cs = effective_nodemask_cpuset(cs);
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	struct css_task_iter it;
	struct task_struct *task;
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	cpuset_being_rebound = cs;		/* causes mpol_dup() rebind */
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	guarantee_online_mems(mems_cs, &newmems);
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