cpuset.c 66.6 KB
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/*
 *  kernel/cpuset.c
 *
 *  Processor and Memory placement constraints for sets of tasks.
 *
 *  Copyright (C) 2003 BULL SA.
 *  Copyright (C) 2004 Silicon Graphics, Inc.
 *
 *  Portions derived from Patrick Mochel's sysfs code.
 *  sysfs is Copyright (c) 2001-3 Patrick Mochel
 *  Portions Copyright (c) 2004 Silicon Graphics, Inc.
 *
 *  2003-10-10 Written by Simon Derr <simon.derr@bull.net>
 *  2003-10-22 Updates by Stephen Hemminger.
 *  2004 May-July Rework by Paul Jackson <pj@sgi.com>
 *
 *  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/config.h>
#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>
#include <linux/module.h>
#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>
#include <linux/slab.h>
#include <linux/smp_lock.h>
#include <linux/spinlock.h>
#include <linux/stat.h>
#include <linux/string.h>
#include <linux/time.h>
#include <linux/backing-dev.h>
#include <linux/sort.h>

#include <asm/uaccess.h>
#include <asm/atomic.h>
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#include <linux/mutex.h>
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#define CPUSET_SUPER_MAGIC		0x27e0eb
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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 {
	unsigned long flags;		/* "unsigned long" so bitops work */
	cpumask_t cpus_allowed;		/* CPUs allowed to tasks in cpuset */
	nodemask_t mems_allowed;	/* Memory Nodes allowed to tasks */

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	/*
	 * Count is atomic so can incr (fork) or decr (exit) without a lock.
	 */
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	atomic_t count;			/* count tasks using this cpuset */

	/*
	 * We link our 'sibling' struct into our parents 'children'.
	 * Our children link their 'sibling' into our 'children'.
	 */
	struct list_head sibling;	/* my parents children */
	struct list_head children;	/* my children */

	struct cpuset *parent;		/* my parent */
	struct dentry *dentry;		/* cpuset fs entry */

	/*
	 * Copy of global cpuset_mems_generation as of the most
	 * recent time this cpuset changed its mems_allowed.
	 */
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	int mems_generation;

	struct fmeter fmeter;		/* memory_pressure filter */
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};

/* bits in struct cpuset flags field */
typedef enum {
	CS_CPU_EXCLUSIVE,
	CS_MEM_EXCLUSIVE,
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	CS_MEMORY_MIGRATE,
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	CS_REMOVED,
	CS_NOTIFY_ON_RELEASE
} cpuset_flagbits_t;

/* convenient tests for these bits */
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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}

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

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

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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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/*
 * Increment this atomic integer everytime any cpuset changes its
 * mems_allowed value.  Users of cpusets can track this generation
 * number, and avoid having to lock and reload mems_allowed unless
 * the cpuset they're using changes generation.
 *
 * A single, global generation is needed because attach_task() could
 * reattach a task to a different cpuset, which must not have its
 * generation numbers aliased with those of that tasks previous cpuset.
 *
 * Generations are needed for mems_allowed because one task cannot
 * modify anothers memory placement.  So we must enable every task,
 * on every visit to __alloc_pages(), to efficiently check whether
 * its current->cpuset->mems_allowed has changed, requiring an update
 * of its current->mems_allowed.
 */
static atomic_t cpuset_mems_generation = ATOMIC_INIT(1);

static struct cpuset top_cpuset = {
	.flags = ((1 << CS_CPU_EXCLUSIVE) | (1 << CS_MEM_EXCLUSIVE)),
	.cpus_allowed = CPU_MASK_ALL,
	.mems_allowed = NODE_MASK_ALL,
	.count = ATOMIC_INIT(0),
	.sibling = LIST_HEAD_INIT(top_cpuset.sibling),
	.children = LIST_HEAD_INIT(top_cpuset.children),
};

static struct vfsmount *cpuset_mount;
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static struct super_block *cpuset_sb;
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/*
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 * We have two global cpuset mutexes below.  They can nest.
 * It is ok to first take manage_mutex, then nest callback_mutex.  We also
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 * require taking task_lock() when dereferencing a tasks cpuset pointer.
 * See "The task_lock() exception", at the end of this comment.
 *
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 * A task must hold both mutexes to modify cpusets.  If a task
 * holds manage_mutex, then it blocks others wanting that mutex,
 * ensuring that it is the only task able to also acquire callback_mutex
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 * and be able to modify cpusets.  It can perform various checks on
 * the cpuset structure first, knowing nothing will change.  It can
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 * also allocate memory while just holding manage_mutex.  While it is
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 * performing these checks, various callback routines can briefly
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 * 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.
 *
 * The task_struct fields mems_allowed and mems_generation may only
 * be accessed in the context of that task, so require no locks.
 *
 * Any task can increment and decrement the count field without lock.
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 * So in general, code holding manage_mutex or callback_mutex can't rely
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 * on the count field not changing.  However, if the count goes to
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 * zero, then only attach_task(), which holds both mutexes, can
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 * increment it again.  Because a count of zero means that no tasks
 * are currently attached, therefore there is no way a task attached
 * to that cpuset can fork (the other way to increment the count).
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 * So code holding manage_mutex or callback_mutex can safely assume that
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 * if the count is zero, it will stay zero.  Similarly, if a task
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 * holds manage_mutex or callback_mutex on a cpuset with zero count, it
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 * knows that the cpuset won't be removed, as cpuset_rmdir() needs
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 * both of those mutexes.
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 *
 * The cpuset_common_file_write handler for operations that modify
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 * the cpuset hierarchy holds manage_mutex across the entire operation,
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 * single threading all such cpuset modifications across the system.
 *
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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.
 *
 * The fork and exit callbacks cpuset_fork() and cpuset_exit(), don't
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 * (usually) take either mutex.  These are the two most performance
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 * critical pieces of code here.  The exception occurs on cpuset_exit(),
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 * when a task in a notify_on_release cpuset exits.  Then manage_mutex
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 * is taken, and if the cpuset count is zero, a usermode call made
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 * to /sbin/cpuset_release_agent with the name of the cpuset (path
 * relative to the root of cpuset file system) as the argument.
 *
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 * A cpuset can only be deleted if both its 'count' of using tasks
 * is zero, and its list of 'children' cpusets is empty.  Since all
 * tasks in the system use _some_ cpuset, and since there is always at
 * least one task in the system (init, pid == 1), therefore, top_cpuset
 * always has either children cpusets and/or using tasks.  So we don't
 * need a special hack to ensure that top_cpuset cannot be deleted.
 *
 * The above "Tale of Two Semaphores" would be complete, but for:
 *
 *	The task_lock() exception
 *
 * The need for this exception arises from the action of attach_task(),
 * which overwrites one tasks cpuset pointer with another.  It does
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 * so using both mutexes, however there are several performance
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 * critical places that need to reference task->cpuset without the
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 * expense of grabbing a system global mutex.  Therefore except as
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 * noted below, when dereferencing or, as in attach_task(), modifying
 * a tasks cpuset pointer we use task_lock(), which acts on a spinlock
 * (task->alloc_lock) already in the task_struct routinely used for
 * such matters.
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 *
 * P.S.  One more locking exception.  RCU is used to guard the
 * update of a tasks cpuset pointer by attach_task() and the
 * access of task->cpuset->mems_generation via that pointer in
 * the routine cpuset_update_task_memory_state().
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 */

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static DEFINE_MUTEX(manage_mutex);
static DEFINE_MUTEX(callback_mutex);
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/*
 * A couple of forward declarations required, due to cyclic reference loop:
 *  cpuset_mkdir -> cpuset_create -> cpuset_populate_dir -> cpuset_add_file
 *  -> cpuset_create_file -> cpuset_dir_inode_operations -> cpuset_mkdir.
 */

static int cpuset_mkdir(struct inode *dir, struct dentry *dentry, int mode);
static int cpuset_rmdir(struct inode *unused_dir, struct dentry *dentry);

static struct backing_dev_info cpuset_backing_dev_info = {
	.ra_pages = 0,		/* No readahead */
	.capabilities	= BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
};

static struct inode *cpuset_new_inode(mode_t mode)
{
	struct inode *inode = new_inode(cpuset_sb);

	if (inode) {
		inode->i_mode = mode;
		inode->i_uid = current->fsuid;
		inode->i_gid = current->fsgid;
		inode->i_blksize = PAGE_CACHE_SIZE;
		inode->i_blocks = 0;
		inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
		inode->i_mapping->backing_dev_info = &cpuset_backing_dev_info;
	}
	return inode;
}

static void cpuset_diput(struct dentry *dentry, struct inode *inode)
{
	/* is dentry a directory ? if so, kfree() associated cpuset */
	if (S_ISDIR(inode->i_mode)) {
		struct cpuset *cs = dentry->d_fsdata;
		BUG_ON(!(is_removed(cs)));
		kfree(cs);
	}
	iput(inode);
}

static struct dentry_operations cpuset_dops = {
	.d_iput = cpuset_diput,
};

static struct dentry *cpuset_get_dentry(struct dentry *parent, const char *name)
{
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	struct dentry *d = lookup_one_len(name, parent, strlen(name));
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	if (!IS_ERR(d))
		d->d_op = &cpuset_dops;
	return d;
}

static void remove_dir(struct dentry *d)
{
	struct dentry *parent = dget(d->d_parent);

	d_delete(d);
	simple_rmdir(parent->d_inode, d);
	dput(parent);
}

/*
 * NOTE : the dentry must have been dget()'ed
 */
static void cpuset_d_remove_dir(struct dentry *dentry)
{
	struct list_head *node;

	spin_lock(&dcache_lock);
	node = dentry->d_subdirs.next;
	while (node != &dentry->d_subdirs) {
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		struct dentry *d = list_entry(node, struct dentry, d_u.d_child);
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		list_del_init(node);
		if (d->d_inode) {
			d = dget_locked(d);
			spin_unlock(&dcache_lock);
			d_delete(d);
			simple_unlink(dentry->d_inode, d);
			dput(d);
			spin_lock(&dcache_lock);
		}
		node = dentry->d_subdirs.next;
	}
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	list_del_init(&dentry->d_u.d_child);
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	spin_unlock(&dcache_lock);
	remove_dir(dentry);
}

static struct super_operations cpuset_ops = {
	.statfs = simple_statfs,
	.drop_inode = generic_delete_inode,
};

static int cpuset_fill_super(struct super_block *sb, void *unused_data,
							int unused_silent)
{
	struct inode *inode;
	struct dentry *root;

	sb->s_blocksize = PAGE_CACHE_SIZE;
	sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
	sb->s_magic = CPUSET_SUPER_MAGIC;
	sb->s_op = &cpuset_ops;
	cpuset_sb = sb;

	inode = cpuset_new_inode(S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR);
	if (inode) {
		inode->i_op = &simple_dir_inode_operations;
		inode->i_fop = &simple_dir_operations;
		/* directories start off with i_nlink == 2 (for "." entry) */
		inode->i_nlink++;
	} else {
		return -ENOMEM;
	}

	root = d_alloc_root(inode);
	if (!root) {
		iput(inode);
		return -ENOMEM;
	}
	sb->s_root = root;
	return 0;
}

static struct super_block *cpuset_get_sb(struct file_system_type *fs_type,
					int flags, const char *unused_dev_name,
					void *data)
{
	return get_sb_single(fs_type, flags, data, cpuset_fill_super);
}

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

/* struct cftype:
 *
 * The files in the cpuset filesystem mostly have a very simple read/write
 * handling, some common function will take care of it. Nevertheless some cases
 * (read tasks) are special and therefore I define this structure for every
 * kind of file.
 *
 *
 * When reading/writing to a file:
 *	- the cpuset to use in file->f_dentry->d_parent->d_fsdata
 *	- the 'cftype' of the file is file->f_dentry->d_fsdata
 */

struct cftype {
	char *name;
	int private;
	int (*open) (struct inode *inode, struct file *file);
	ssize_t (*read) (struct file *file, char __user *buf, size_t nbytes,
							loff_t *ppos);
	int (*write) (struct file *file, const char __user *buf, size_t nbytes,
							loff_t *ppos);
	int (*release) (struct inode *inode, struct file *file);
};

static inline struct cpuset *__d_cs(struct dentry *dentry)
{
	return dentry->d_fsdata;
}

static inline struct cftype *__d_cft(struct dentry *dentry)
{
	return dentry->d_fsdata;
}

/*
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 * Call with manage_mutex held.  Writes path of cpuset into buf.
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 * Returns 0 on success, -errno on error.
 */

static int cpuset_path(const struct cpuset *cs, char *buf, int buflen)
{
	char *start;

	start = buf + buflen;

	*--start = '\0';
	for (;;) {
		int len = cs->dentry->d_name.len;
		if ((start -= len) < buf)
			return -ENAMETOOLONG;
		memcpy(start, cs->dentry->d_name.name, len);
		cs = cs->parent;
		if (!cs)
			break;
		if (!cs->parent)
			continue;
		if (--start < buf)
			return -ENAMETOOLONG;
		*start = '/';
	}
	memmove(buf, start, buf + buflen - start);
	return 0;
}

/*
 * Notify userspace when a cpuset is released, by running
 * /sbin/cpuset_release_agent with the name of the cpuset (path
 * relative to the root of cpuset file system) as the argument.
 *
 * Most likely, this user command will try to rmdir this cpuset.
 *
 * This races with the possibility that some other task will be
 * attached to this cpuset before it is removed, or that some other
 * user task will 'mkdir' a child cpuset of this cpuset.  That's ok.
 * The presumed 'rmdir' will fail quietly if this cpuset is no longer
 * unused, and this cpuset will be reprieved from its death sentence,
 * to continue to serve a useful existence.  Next time it's released,
 * we will get notified again, if it still has 'notify_on_release' set.
 *
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 * The final arg to call_usermodehelper() is 0, which means don't
 * wait.  The separate /sbin/cpuset_release_agent task is forked by
 * call_usermodehelper(), then control in this thread returns here,
 * without waiting for the release agent task.  We don't bother to
 * wait because the caller of this routine has no use for the exit
 * status of the /sbin/cpuset_release_agent task, so no sense holding
 * our caller up for that.
 *
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 * When we had only one cpuset mutex, we had to call this
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 * without holding it, to avoid deadlock when call_usermodehelper()
 * allocated memory.  With two locks, we could now call this while
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 * holding manage_mutex, but we still don't, so as to minimize
 * the time manage_mutex is held.
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 */

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static void cpuset_release_agent(const char *pathbuf)
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{
	char *argv[3], *envp[3];
	int i;

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	if (!pathbuf)
		return;

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	i = 0;
	argv[i++] = "/sbin/cpuset_release_agent";
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	argv[i++] = (char *)pathbuf;
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	argv[i] = NULL;

	i = 0;
	/* minimal command environment */
	envp[i++] = "HOME=/";
	envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
	envp[i] = NULL;

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	call_usermodehelper(argv[0], argv, envp, 0);
	kfree(pathbuf);
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}

/*
 * Either cs->count of using tasks transitioned to zero, or the
 * cs->children list of child cpusets just became empty.  If this
 * cs is notify_on_release() and now both the user count is zero and
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 * the list of children is empty, prepare cpuset path in a kmalloc'd
 * buffer, to be returned via ppathbuf, so that the caller can invoke
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 * cpuset_release_agent() with it later on, once manage_mutex is dropped.
 * Call here with manage_mutex held.
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 *
 * This check_for_release() routine is responsible for kmalloc'ing
 * pathbuf.  The above cpuset_release_agent() is responsible for
 * kfree'ing pathbuf.  The caller of these routines is responsible
 * for providing a pathbuf pointer, initialized to NULL, then
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 * calling check_for_release() with manage_mutex held and the address
 * of the pathbuf pointer, then dropping manage_mutex, then calling
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 * cpuset_release_agent() with pathbuf, as set by check_for_release().
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 */

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static void check_for_release(struct cpuset *cs, char **ppathbuf)
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{
	if (notify_on_release(cs) && atomic_read(&cs->count) == 0 &&
	    list_empty(&cs->children)) {
		char *buf;

		buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
		if (!buf)
			return;
		if (cpuset_path(cs, buf, PAGE_SIZE) < 0)
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			kfree(buf);
		else
			*ppathbuf = buf;
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	}
}

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

static void guarantee_online_cpus(const struct cpuset *cs, cpumask_t *pmask)
{
	while (cs && !cpus_intersects(cs->cpus_allowed, cpu_online_map))
		cs = cs->parent;
	if (cs)
		cpus_and(*pmask, cs->cpus_allowed, cpu_online_map);
	else
		*pmask = cpu_online_map;
	BUG_ON(!cpus_intersects(*pmask, cpu_online_map));
}

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

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

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/**
 * cpuset_update_task_memory_state - update task memory placement
 *
 * If the current tasks cpusets mems_allowed changed behind our
 * backs, update current->mems_allowed, mems_generation and task NUMA
 * mempolicy to the new value.
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 *
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 * Task mempolicy is updated by rebinding it relative to the
 * current->cpuset if a task has its memory placement changed.
 * Do not call this routine if in_interrupt().
 *
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 * Call without callback_mutex or task_lock() held.  May be called
 * with or without manage_mutex held.  Doesn't need task_lock to guard
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 * against another task changing a non-NULL cpuset pointer to NULL,
 * as that is only done by a task on itself, and if the current task
 * is here, it is not simultaneously in the exit code NULL'ing its
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 * cpuset pointer.  This routine also might acquire callback_mutex and
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 * current->mm->mmap_sem during call.
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 *
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 * Reading current->cpuset->mems_generation doesn't need task_lock
 * to guard the current->cpuset derefence, because it is guarded
 * from concurrent freeing of current->cpuset by attach_task(),
 * using RCU.
 *
 * The rcu_dereference() is technically probably not needed,
 * as I don't actually mind if I see a new cpuset pointer but
 * an old value of mems_generation.  However this really only
 * matters on alpha systems using cpusets heavily.  If I dropped
 * that rcu_dereference(), it would save them a memory barrier.
 * For all other arch's, rcu_dereference is a no-op anyway, and for
 * alpha systems not using cpusets, another planned optimization,
 * avoiding the rcu critical section for tasks in the root cpuset
 * which is statically allocated, so can't vanish, will make this
 * irrelevant.  Better to use RCU as intended, than to engage in
 * some cute trick to save a memory barrier that is impossible to
 * test, for alpha systems using cpusets heavily, which might not
 * even exist.
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 *
 * This routine is needed to update the per-task mems_allowed data,
 * within the tasks context, when it is trying to allocate memory
 * (in various mm/mempolicy.c routines) and notices that some other
 * task has been modifying its cpuset.
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 */

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void cpuset_update_task_memory_state(void)
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{
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	int my_cpusets_mem_gen;
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	struct task_struct *tsk = current;
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	struct cpuset *cs;
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	if (tsk->cpuset == &top_cpuset) {
		/* Don't need rcu for top_cpuset.  It's never freed. */
		my_cpusets_mem_gen = top_cpuset.mems_generation;
	} else {
		rcu_read_lock();
		cs = rcu_dereference(tsk->cpuset);
		my_cpusets_mem_gen = cs->mems_generation;
		rcu_read_unlock();
	}
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	if (my_cpusets_mem_gen != tsk->cpuset_mems_generation) {
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		mutex_lock(&callback_mutex);
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		task_lock(tsk);
		cs = tsk->cpuset;	/* Maybe changed when task not locked */
		guarantee_online_mems(cs, &tsk->mems_allowed);
		tsk->cpuset_mems_generation = cs->mems_generation;
		task_unlock(tsk);
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		mutex_unlock(&callback_mutex);
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		mpol_rebind_task(tsk, &tsk->mems_allowed);
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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 manage_mutex.
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 */

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

/*
 * 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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 * manage_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.
 */

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

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

	/* Remaining checks don't apply to root cpuset */
	if ((par = cur->parent) == NULL)
		return 0;

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

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

	return 0;
}

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/*
 * For a given cpuset cur, partition the system as follows
 * a. All cpus in the parent cpuset's cpus_allowed that are not part of any
 *    exclusive child cpusets
 * b. All cpus in the current cpuset's cpus_allowed that are not part of any
 *    exclusive child cpusets
 * Build these two partitions by calling partition_sched_domains
 *
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 * Call with manage_mutex held.  May nest a call to the
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 * lock_cpu_hotplug()/unlock_cpu_hotplug() pair.
 */
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static void update_cpu_domains(struct cpuset *cur)
{
	struct cpuset *c, *par = cur->parent;
	cpumask_t pspan, cspan;

	if (par == NULL || cpus_empty(cur->cpus_allowed))
		return;

	/*
	 * Get all cpus from parent's cpus_allowed not part of exclusive
	 * children
	 */
	pspan = par->cpus_allowed;
	list_for_each_entry(c, &par->children, sibling) {
		if (is_cpu_exclusive(c))
			cpus_andnot(pspan, pspan, c->cpus_allowed);
	}
	if (is_removed(cur) || !is_cpu_exclusive(cur)) {
		cpus_or(pspan, pspan, cur->cpus_allowed);
		if (cpus_equal(pspan, cur->cpus_allowed))
			return;
		cspan = CPU_MASK_NONE;
	} else {
		if (cpus_empty(pspan))
			return;
		cspan = cur->cpus_allowed;
		/*
		 * Get all cpus from current cpuset's cpus_allowed not part
		 * of exclusive children
		 */
		list_for_each_entry(c, &cur->children, sibling) {
			if (is_cpu_exclusive(c))
				cpus_andnot(cspan, cspan, c->cpus_allowed);
		}
	}

	lock_cpu_hotplug();
	partition_sched_domains(&pspan, &cspan);
	unlock_cpu_hotplug();
}

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/*
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 * Call with manage_mutex held.  May take callback_mutex during call.
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 */

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static int update_cpumask(struct cpuset *cs, char *buf)
{
	struct cpuset trialcs;
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	int retval, cpus_unchanged;
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	trialcs = *cs;
	retval = cpulist_parse(buf, trialcs.cpus_allowed);
	if (retval < 0)
		return retval;
	cpus_and(trialcs.cpus_allowed, trialcs.cpus_allowed, cpu_online_map);
	if (cpus_empty(trialcs.cpus_allowed))
		return -ENOSPC;
	retval = validate_change(cs, &trialcs);
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	if (retval < 0)
		return retval;
	cpus_unchanged = cpus_equal(cs->cpus_allowed, trialcs.cpus_allowed);
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	mutex_lock(&callback_mutex);
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	cs->cpus_allowed = trialcs.cpus_allowed;
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	mutex_unlock(&callback_mutex);
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	if (is_cpu_exclusive(cs) && !cpus_unchanged)
		update_cpu_domains(cs);
	return 0;
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}

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/*
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 * Handle user request to change the 'mems' memory placement
 * of a cpuset.  Needs to validate the request, update the
 * cpusets mems_allowed and mems_generation, and for each
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 * task in the cpuset, rebind any vma mempolicies and if
 * the cpuset is marked 'memory_migrate', migrate the tasks
 * pages to the new memory.
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 *
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 * Call with manage_mutex held.  May take callback_mutex during call.
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 * Will take tasklist_lock, scan tasklist for tasks in cpuset cs,
 * lock each such tasks mm->mmap_sem, scan its vma's and rebind
 * their mempolicies to the cpusets new mems_allowed.
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 */

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static int update_nodemask(struct cpuset *cs, char *buf)
{
	struct cpuset trialcs;
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	nodemask_t oldmem;
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	struct task_struct *g, *p;
	struct mm_struct **mmarray;
	int i, n, ntasks;
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	int migrate;
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	int fudge;
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	int retval;

	trialcs = *cs;
	retval = nodelist_parse(buf, trialcs.mems_allowed);
	if (retval < 0)
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		goto done;
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	nodes_and(trialcs.mems_allowed, trialcs.mems_allowed, node_online_map);
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	oldmem = cs->mems_allowed;
	if (nodes_equal(oldmem, trialcs.mems_allowed)) {
		retval = 0;		/* Too easy - nothing to do */
		goto done;
	}
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	if (nodes_empty(trialcs.mems_allowed)) {
		retval = -ENOSPC;
		goto done;
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	}
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	retval = validate_change(cs, &trialcs);
	if (retval < 0)
		goto done;

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	mutex_lock(&callback_mutex);
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	cs->mems_allowed = trialcs.mems_allowed;
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	cs->mems_generation = atomic_inc_return(&cpuset_mems_generation);
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	mutex_unlock(&callback_mutex);
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	set_cpuset_being_rebound(cs);		/* causes mpol_copy() rebind */

	fudge = 10;				/* spare mmarray[] slots */
	fudge += cpus_weight(cs->cpus_allowed);	/* imagine one fork-bomb/cpu */
	retval = -ENOMEM;

	/*
	 * Allocate mmarray[] to hold mm reference for each task
	 * in cpuset cs.  Can't kmalloc GFP_KERNEL while holding
	 * tasklist_lock.  We could use GFP_ATOMIC, but with a
	 * few more lines of code, we can retry until we get a big
	 * enough mmarray[] w/o using GFP_ATOMIC.
	 */
	while (1) {
		ntasks = atomic_read(&cs->count);	/* guess */
		ntasks += fudge;
		mmarray = kmalloc(ntasks * sizeof(*mmarray), GFP_KERNEL);
		if (!mmarray)
			goto done;
		write_lock_irq(&tasklist_lock);		/* block fork */
		if (atomic_read(&cs->count) <= ntasks)
			break;				/* got enough */
		write_unlock_irq(&tasklist_lock);	/* try again */
		kfree(mmarray);
	}

	n = 0;

	/* Load up mmarray[] with mm reference for each task in cpuset. */
	do_each_thread(g, p) {
		struct mm_struct *mm;

		if (n >= ntasks) {
			printk(KERN_WARNING
				"Cpuset mempolicy rebind incomplete.\n");
			continue;
		}
		if (p->cpuset != cs)
			continue;
		mm = get_task_mm(p);
		if (!mm)
			continue;
		mmarray[n++] = mm;
	} while_each_thread(g, p);
	write_unlock_irq(&tasklist_lock);

	/*
	 * Now that we've dropped the tasklist spinlock, we can
	 * rebind the vma mempolicies of each mm in mmarray[] to their
	 * new cpuset, and release that mm.  The mpol_rebind_mm()
	 * call takes mmap_sem, which we couldn't take while holding
	 * tasklist_lock.  Forks can happen again now - the mpol_copy()
	 * cpuset_being_rebound check will catch such forks, and rebind
	 * their vma mempolicies too.  Because we still hold the global
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	 * be contending for the global variable cpuset_being_rebound.
	 * It's ok if we rebind the same mm twice; mpol_rebind_mm()
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	 * is idempotent.  Also migrate pages in each mm to new nodes.
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	 */
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	migrate = is_memory_migrate(cs);
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	for (i = 0; i < n; i++) {
		struct mm_struct *mm = mmarray[i];

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

	/* We're done rebinding vma's to this cpusets new mems_allowed. */
	kfree(mmarray);
	set_cpuset_being_rebound(NULL);
	retval = 0;
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done:
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	return retval;
}

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/*
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 * Call with manage_mutex held.
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 */

static int update_memory_pressure_enabled(struct cpuset *cs, char *buf)
{
	if (simple_strtoul(buf, NULL, 10) != 0)
		cpuset_memory_pressure_enabled = 1;
	else
		cpuset_memory_pressure_enabled = 0;
	return 0;
}

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/*
 * update_flag - read a 0 or a 1 in a file and update associated flag
 * bit:	the bit to update (CS_CPU_EXCLUSIVE, CS_MEM_EXCLUSIVE,
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 *				CS_NOTIFY_ON_RELEASE, CS_MEMORY_MIGRATE)
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 * cs:	the cpuset to update
 * buf:	the buffer where we read the 0 or 1
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 *
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 * Call with manage_mutex held.
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 */

static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs, char *buf)
{
	int turning_on;
	struct cpuset trialcs;
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	int err, cpu_exclusive_changed;
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	turning_on = (simple_strtoul(buf, NULL, 10) != 0);

	trialcs = *cs;
	if (turning_on)
		set_bit(bit, &trialcs.flags);
	else
		clear_bit(bit, &trialcs.flags);

	err = validate_change(cs, &trialcs);
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	if (err < 0)
		return err;
	cpu_exclusive_changed =
		(is_cpu_exclusive(cs) != is_cpu_exclusive(&trialcs));
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	mutex_lock(&callback_mutex);
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	if (turning_on)
		set_bit(bit, &cs->flags);
	else
		clear_bit(bit, &cs->flags);
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	mutex_unlock(&callback_mutex);
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	if (cpu_exclusive_changed)
                update_cpu_domains(cs);
	return 0;
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}

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

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

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

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

	if (ticks == 0)
		return;

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

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

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

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

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

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/*
 * Attack task specified by pid in 'pidbuf' to cpuset 'cs', possibly
 * writing the path of the old cpuset in 'ppathbuf' if it needs to be
 * notified on release.
 *
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 * Call holding manage_mutex.  May take callback_mutex and task_lock of
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 * the task 'pid' during call.
 */

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static int attach_task(struct cpuset *cs, char *pidbuf, char **ppathbuf)
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{
	pid_t pid;
	struct task_struct *tsk;
	struct cpuset *oldcs;
	cpumask_t cpus;
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	nodemask_t from, to;
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	struct mm_struct *mm;
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	if (sscanf(pidbuf, "%d", &pid) != 1)
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		return -EIO;
	if (cpus_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed))
		return -ENOSPC;

	if (pid) {
		read_lock(&tasklist_lock);

		tsk = find_task_by_pid(pid);
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		if (!tsk || tsk->flags & PF_EXITING) {
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			read_unlock(&tasklist_lock);
			return -ESRCH;
		}

		get_task_struct(tsk);
		read_unlock(&tasklist_lock);

		if ((current->euid) && (current->euid != tsk->uid)
		    && (current->euid != tsk->suid)) {
			put_task_struct(tsk);
			return -EACCES;
		}
	} else {
		tsk = current;
		get_task_struct(tsk);
	}

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	mutex_lock(&callback_mutex);
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	task_lock(tsk);
	oldcs = tsk->cpuset;
	if (!oldcs) {
		task_unlock(tsk);
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		mutex_unlock(&callback_mutex);
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		put_task_struct(tsk);
		return -ESRCH;
	}
	atomic_inc(&cs->count);
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	rcu_assign_pointer(tsk->cpuset, cs);
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	task_unlock(tsk);

	guarantee_online_cpus(cs, &cpus);
	set_cpus_allowed(tsk, cpus);

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	from = oldcs->mems_allowed;
	to = cs->mems_allowed;

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	mutex_unlock(&callback_mutex);
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	mm = get_task_mm(tsk);
	if (mm) {
		mpol_rebind_mm(mm, &to);
		mmput(mm);
	}

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	if (is_memory_migrate(cs))
		do_migrate_pages(tsk->mm, &from, &to, MPOL_MF_MOVE_ALL);
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	put_task_struct(tsk);
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	synchronize_rcu();
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	if (atomic_dec_and_test(&oldcs->count))
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		check_for_release(oldcs, ppathbuf);
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	return 0;
}

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

typedef enum {
	FILE_ROOT,
	FILE_DIR,
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	FILE_MEMORY_MIGRATE,
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	FILE_CPULIST,
	FILE_MEMLIST,
	FILE_CPU_EXCLUSIVE,
	FILE_MEM_EXCLUSIVE,
	FILE_NOTIFY_ON_RELEASE,
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	FILE_MEMORY_PRESSURE_ENABLED,
	FILE_MEMORY_PRESSURE,
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	FILE_TASKLIST,
} cpuset_filetype_t;

static ssize_t cpuset_common_file_write(struct file *file, const char __user *userbuf,
					size_t nbytes, loff_t *unused_ppos)
{
	struct cpuset *cs = __d_cs(file->f_dentry->d_parent);
	struct cftype *cft = __d_cft(file->f_dentry);
	cpuset_filetype_t type = cft->private;
	char *buffer;
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	char *pathbuf = NULL;
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	int retval = 0;

	/* Crude upper limit on largest legitimate cpulist user might write. */
	if (nbytes > 100 + 6 * NR_CPUS)
		return -E2BIG;

	/* +1 for nul-terminator */
	if ((buffer = kmalloc(nbytes + 1, GFP_KERNEL)) == 0)
		return -ENOMEM;

	if (copy_from_user(buffer, userbuf, nbytes)) {
		retval = -EFAULT;
		goto out1;
	}
	buffer[nbytes] = 0;	/* nul-terminate */

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	mutex_lock(&manage_mutex);
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	if (is_removed(cs)) {
		retval = -ENODEV;
		goto out2;
	}

	switch (type) {
	case FILE_CPULIST:
		retval = update_cpumask(cs, buffer);
		break;
	case FILE_MEMLIST:
		retval = update_nodemask(cs, buffer);
		break;
	case FILE_CPU_EXCLUSIVE:
		retval = update_flag(CS_CPU_EXCLUSIVE, cs, buffer);
		break;
	case FILE_MEM_EXCLUSIVE:
		retval = update_flag(CS_MEM_EXCLUSIVE, cs, buffer);
		break;
	case FILE_NOTIFY_ON_RELEASE:
		retval = update_flag(CS_NOTIFY_ON_RELEASE, cs, buffer);
		break;
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	case FILE_MEMORY_MIGRATE:
		retval = update_flag(CS_MEMORY_MIGRATE, cs, buffer);
		break;
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	case FILE_MEMORY_PRESSURE_ENABLED:
		retval = update_memory_pressure_enabled(cs, buffer);
		break;
	case FILE_MEMORY_PRESSURE:
		retval = -EACCES;
		break;
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	case FILE_TASKLIST:
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		retval = attach_task(cs, buffer, &pathbuf);
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		break;
	default:
		retval = -EINVAL;
		goto out2;
	}

	if (retval == 0)
		retval = nbytes;
out2:
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	mutex_unlock(&manage_mutex);
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	cpuset_release_agent(pathbuf);
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out1:
	kfree(buffer);
	return retval;
}

static ssize_t cpuset_file_write(struct file *file, const char __user *buf,
						size_t nbytes, loff_t *ppos)
{
	ssize_t retval = 0;
	struct cftype *cft = __d_cft(file->f_dentry);
	if (!cft)
		return -ENODEV;

	/* special function ? */
	if (cft->write)
		retval = cft->write(file, buf, nbytes, ppos);
	else
		retval = cpuset_common_file_write(file, buf, nbytes, ppos);

	return retval;
}

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

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

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

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

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	mutex_lock(&callback_mutex);
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	mask = cs->mems_allowed;
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	mutex_unlock(&callback_mutex);
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	return nodelist_scnprintf(page, PAGE_SIZE, mask);
}

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

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

	s = page;

	switch (type) {
	case FILE_CPULIST:
		s += cpuset_sprintf_cpulist(s, cs);
		break;
	case FILE_MEMLIST:
		s += cpuset_sprintf_memlist(s, cs);
		break;
	case FILE_CPU_EXCLUSIVE:
		*s++ = is_cpu_exclusive(cs) ? '1' : '0';
		break;
	case FILE_MEM_EXCLUSIVE:
		*s++ = is_mem_exclusive(cs) ? '1' : '0';
		break;
	case FILE_NOTIFY_ON_RELEASE:
		*s++ = notify_on_release(cs) ? '1' : '0';
		break;
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	case FILE_MEMORY_MIGRATE:
		*s++ = is_memory_migrate(cs) ? '1' : '0';
		break;
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	case FILE_MEMORY_PRESSURE_ENABLED:
		*s++ = cpuset_memory_pressure_enabled ? '1' : '0';
		break;
	case FILE_MEMORY_PRESSURE:
		s += sprintf(s, "%d", fmeter_getrate(&cs->fmeter));
		break;
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	default:
		retval = -EINVAL;
		goto out;
	}
	*s++ = '\n';

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

static ssize_t cpuset_file_read(struct file *file, char __user *buf, size_t nbytes,
								loff_t *ppos)
{
	ssize_t retval = 0;
	struct cftype *cft = __d_cft(file->f_dentry);
	if (!cft)
		return -ENODEV;

	/* special function ? */
	if (cft->read)
		retval = cft->read(file, buf, nbytes, ppos);
	else
		retval = cpuset_common_file_read(file, buf, nbytes, ppos);

	return retval;
}

static int cpuset_file_open(struct inode *inode, struct file *file)
{
	int err;
	struct cftype *cft;

	err = generic_file_open(inode, file);
	if (err)
		return err;

	cft = __d_cft(file->f_dentry);
	if (!cft)
		return -ENODEV;
	if (cft->open)
		err = cft->open(inode, file);
	else
		err = 0;

	return err;
}

static int cpuset_file_release(struct inode *inode, struct file *file)
{
	struct cftype *cft = __d_cft(file->f_dentry);
	if (cft->release)
		return cft->release(inode, file);
	return 0;
}

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/*
 * cpuset_rename - Only allow simple rename of directories in place.
 */
static int cpuset_rename(struct inode *old_dir, struct dentry *old_dentry,
                  struct inode *new_dir, struct dentry *new_dentry)
{
	if (!S_ISDIR(old_dentry->d_inode->i_mode))
		return -ENOTDIR;
	if (new_dentry->d_inode)
		return -EEXIST;
	if (old_dir != new_dir)
		return -EIO;
	return simple_rename(old_dir, old_dentry, new_dir, new_dentry);
}

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static struct file_operations cpuset_file_operations = {
	.read = cpuset_file_read,
	.write = cpuset_file_write,
	.llseek = generic_file_llseek,
	.open = cpuset_file_open,
	.release = cpuset_file_release,
};

static struct inode_operations cpuset_dir_inode_operations = {
	.lookup = simple_lookup,
	.mkdir = cpuset_mkdir,
	.rmdir = cpuset_rmdir,
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	.rename = cpuset_rename,
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};

static int cpuset_create_file(struct dentry *dentry, int mode)
{
	struct inode *inode;

	if (!dentry)
		return -ENOENT;
	if (dentry->d_inode)
		return -EEXIST;

	inode = cpuset_new_inode(mode);
	if (!inode)
		return -ENOMEM;

	if (S_ISDIR(mode)) {
		inode->i_op = &cpuset_dir_inode_operations;
		inode->i_fop = &simple_dir_operations;

		/* start off with i_nlink == 2 (for "." entry) */
		inode->i_nlink++;
	} else if (S_ISREG(mode)) {
		inode->i_size = 0;
		inode->i_fop = &cpuset_file_operations;
	}

	d_instantiate(dentry, inode);
	dget(dentry);	/* Extra count - pin the dentry in core */
	return 0;
}

/*
 *	cpuset_create_dir - create a directory for an object.
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 *	cs:	the cpuset we create the directory for.
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 *		It must have a valid ->parent field
 *		And we are going to fill its ->dentry field.
 *	name:	The name to give to the cpuset directory. Will be copied.
 *	mode:	mode to set on new directory.
 */

static int cpuset_create_dir(struct cpuset *cs, const char *name, int mode)
{
	struct dentry *dentry = NULL;
	struct dentry *parent;
	int error = 0;

	parent = cs->parent->dentry;
	dentry = cpuset_get_dentry(parent, name);
	if (IS_ERR(dentry))
		return PTR_ERR(dentry);
	error = cpuset_create_file(dentry, S_IFDIR | mode);
	if (!error) {
		dentry->d_fsdata = cs;
		parent->d_inode->i_nlink++;
		cs->dentry = dentry;
	}
	dput(dentry);

	return error;
}

static int cpuset_add_file(struct dentry *dir, const struct cftype *cft)
{
	struct dentry *dentry;
	int error;

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	mutex_lock(&dir->d_inode->i_mutex);
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	dentry = cpuset_get_dentry(dir, cft->name);
	if (!IS_ERR(dentry)) {
		error = cpuset_create_file(dentry, 0644 | S_IFREG);
		if (!error)
			dentry->d_fsdata = (void *)cft;
		dput(dentry);
	} else
		error = PTR_ERR(dentry);
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	mutex_unlock(&dir->d_inode->i_mutex);
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	return error;
}

/*
 * Stuff for reading the 'tasks' file.
 *
 * Reading this file can return large amounts of data if a cpuset has
 * *lots* of attached tasks. So it may need several calls to read(),
 * but we cannot guarantee that the information we produce is correct
 * unless we produce it entirely atomically.
 *
 * Upon tasks file open(), a struct ctr_struct is allocated, that
 * will have a pointer to an array (also allocated here).  The struct
 * ctr_struct * is stored in file->private_data.  Its resources will
 * be freed by release() when the file is closed.  The array is used
 * to sprintf the PIDs and then used by read().
 */

/* cpusets_tasks_read array */

struct ctr_struct {
	char *buf;
	int bufsz;
};

/*
 * Load into 'pidarray' up to 'npids' of the tasks using cpuset 'cs'.
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 * Return actual number of pids loaded.  No need to task_lock(p)
 * when reading out p->cpuset, as we don't really care if it changes
 * on the next cycle, and we are not going to try to dereference it.
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 */
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static int pid_array_load(pid_t *pidarray, int npids, struct cpuset *cs)
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{
	int n = 0;
	struct task_struct *g, *p;

	read_lock(&tasklist_lock);

	do_each_thread(g, p) {
		if (p->cpuset == cs) {
			pidarray[n++] = p->pid;
			if (unlikely(n == npids))
				goto array_full;
		}
	} while_each_thread(g, p);

array_full:
	read_unlock(&tasklist_lock);
	return n;
}

static int cmppid(const void *a, const void *b)
{
	return *(pid_t *)a - *(pid_t *)b;
}

/*
 * Convert array 'a' of 'npids' pid_t's to a string of newline separated
 * decimal pids in 'buf'.  Don't write more than 'sz' chars, but return
 * count 'cnt' of how many chars would be written if buf were large enough.
 */
static int pid_array_to_buf(char *buf, int sz, pid_t *a, int npids)
{
	int cnt = 0;
	int i;

	for (i = 0; i < npids; i++)
		cnt += snprintf(buf + cnt, max(sz - cnt, 0), "%d\n", a[i]);
	return cnt;
}

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/*
 * Handle an open on 'tasks' file.  Prepare a buffer listing the
 * process id's of tasks currently attached to the cpuset being opened.
 *
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 */
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