hotplug cpu: move tasks in empty cpusets to parent

					struct cgroup_iter *it);

void cgroup_iter_end(struct cgroup *cont, struct cgroup_iter *it);

int cgroup_scan_tasks(struct cgroup_scanner *scan);

int cgroup_attach_task(struct cgroup *, struct task_struct *);

#else /* !CONFIG_CGROUPS */

 * Any task can increment and decrement the count field without lock.

 * So in general, code holding cgroup_mutex can't rely on the count

 * field not changing.  However, if the count goes to zero, then only

 * attach_task() can increment it again.  Because a count of zero

 * cgroup_attach_task() can 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 cgroup can fork (the other way to

 * increment the count).  So code holding cgroup_mutex can safely

 *	The task_lock() exception

 *

 * The need for this exception arises from the action of

 * attach_task(), which overwrites one tasks cgroup pointer with

 * cgroup_attach_task(), which overwrites one tasks cgroup pointer with

 * another.  It does so using cgroup_mutexe, however there are

 * several performance critical places that need to reference

 * task->cgroup without the expense of grabbing a system global

 * mutex.  Therefore except as noted below, when dereferencing or, as

 * in attach_task(), modifying a task'ss cgroup pointer we use

 * in cgroup_attach_task(), modifying a task'ss cgroup pointer we use

 * task_lock(), which acts on a spinlock (task->alloc_lock) already in

 * the task_struct routinely used for such matters.

 *

 * P.S.  One more locking exception.  RCU is used to guard the

 * update of a tasks cgroup pointer by attach_task()

 * update of a tasks cgroup pointer by cgroup_attach_task()

 */

/**

 * Call holding cgroup_mutex.  May take task_lock of

 * the task 'pid' during call.

 */

static int attach_task(struct cgroup *cgrp, struct task_struct *tsk)

int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)

{

	int retval = 0;

	struct cgroup_subsys *ss;

		get_task_struct(tsk);

	}

	ret = attach_task(cgrp, tsk);

	ret = cgroup_attach_task(cgrp, tsk);

	put_task_struct(tsk);

	return ret;

}

 *  - Used for /proc/<pid>/cgroup.

 *  - No need to task_lock(tsk) on this tsk->cgroup reference, as it

 *    doesn't really matter if tsk->cgroup changes after we read it,

 *    and we take cgroup_mutex, keeping attach_task() from changing it

 *    and we take cgroup_mutex, keeping cgroup_attach_task() from changing it

 *    anyway.  No need to check that tsk->cgroup != NULL, thanks to

 *    the_top_cgroup_hack in cgroup_exit(), which sets an exiting tasks

 *    cgroup to top_cgroup.

 * A pointer to the shared css_set was automatically copied in

 * fork.c by dup_task_struct().  However, we ignore that copy, since

 * it was not made under the protection of RCU or cgroup_mutex, so

 * might no longer be a valid cgroup pointer.  attach_task() might

 * might no longer be a valid cgroup pointer.  cgroup_attach_task() might

 * have already changed current->cgroups, allowing the previously

 * referenced cgroup group to be removed and freed.

 *

 *    attach us to a different cgroup, decrementing the count on

 *    the first cgroup that we never incremented.  But in this case,

 *    top_cgroup isn't going away, and either task has PF_EXITING set,

 *    which wards off any attach_task() attempts, or task is a failed

 *    fork, never visible to attach_task.

 *    which wards off any cgroup_attach_task() attempts, or task is a failed

 *    fork, never visible to cgroup_attach_task.

 *

 */

void cgroup_exit(struct task_struct *tsk, int run_callbacks)

	}

	/* All seems fine. Finish by moving the task into the new cgroup */

	ret = attach_task(child, tsk);

	ret = cgroup_attach_task(child, tsk);

	mutex_unlock(&cgroup_mutex);

 out_release:

#include <asm/atomic.h>

#include <linux/mutex.h>

#include <linux/kfifo.h>

#include <linux/workqueue.h>

#include <linux/cgroup.h>

/*

 * Tracks how many cpusets are currently defined in system.

	/* partition number for rebuild_sched_domains() */

	int pn;

	/* used for walking a cpuset heirarchy */

	struct list_head stack_list;

};

/* Retrieve the cpuset for a cgroup */

	return container_of(task_subsys_state(task, cpuset_subsys_id),

			    struct cpuset, css);

}

struct cpuset_hotplug_scanner {

	struct cgroup_scanner scan;

	struct cgroup *to;

};

/* bits in struct cpuset flags field */

typedef enum {

	return 0;

}

/**

 * cpuset_do_move_task - move a given task to another cpuset

 * @tsk: pointer to task_struct the task to move

 * @scan: struct cgroup_scanner contained in its struct cpuset_hotplug_scanner

 *

 * Called by cgroup_scan_tasks() for each task in a cgroup.

 * Return nonzero to stop the walk through the tasks.

 */

void cpuset_do_move_task(struct task_struct *tsk, struct cgroup_scanner *scan)

{

	struct cpuset_hotplug_scanner *chsp;

	chsp = container_of(scan, struct cpuset_hotplug_scanner, scan);

	cgroup_attach_task(chsp->to, tsk);

}

/**

 * move_member_tasks_to_cpuset - move tasks from one cpuset to another

 * @from: cpuset in which the tasks currently reside

 * @to: cpuset to which the tasks will be moved

 *

 * Called with manage_sem held

 * callback_mutex must not be held, as attach_task() will take it.

 *

 * The cgroup_scan_tasks() function will scan all the tasks in a cgroup,

 * calling callback functions for each.

 */

static void move_member_tasks_to_cpuset(struct cpuset *from, struct cpuset *to)

{

	struct cpuset_hotplug_scanner scan;

	scan.scan.cg = from->css.cgroup;

	scan.scan.test_task = NULL; /* select all tasks in cgroup */

	scan.scan.process_task = cpuset_do_move_task;

	scan.scan.heap = NULL;

	scan.to = to->css.cgroup;

	if (cgroup_scan_tasks((struct cgroup_scanner *)&scan))

		printk(KERN_ERR "move_member_tasks_to_cpuset: "

				"cgroup_scan_tasks failed\n");

}

/*

 * If common_cpu_mem_hotplug_unplug(), below, unplugs any CPUs

 * or memory nodes, we need to walk over the cpuset hierarchy,

 * removing that CPU or node from all cpusets.  If this removes the

 * last CPU or node from a cpuset, then the guarantee_online_cpus()

 * or guarantee_online_mems() code will use that emptied cpusets

 * parent online CPUs or nodes.  Cpusets that were already empty of

 * CPUs or nodes are left empty.

 *

 * This routine is intentionally inefficient in a couple of regards.

 * It will check all cpusets in a subtree even if the top cpuset of

 * the subtree has no offline CPUs or nodes.  It checks both CPUs and

 * nodes, even though the caller could have been coded to know that

 * only one of CPUs or nodes needed to be checked on a given call.

 * This was done to minimize text size rather than cpu cycles.

 * last CPU or node from a cpuset, then move the tasks in the empty

 * cpuset to its next-highest non-empty parent.

 *

 * Call with both manage_mutex and callback_mutex held.

 * The parent cpuset has some superset of the 'mems' nodes that the

 * newly empty cpuset held, so no migration of memory is necessary.

 *

 * Recursive, on depth of cpuset subtree.

 * Called with both manage_sem and callback_sem held

 */

static void remove_tasks_in_empty_cpuset(struct cpuset *cs)

{

	struct cpuset *parent;

	/* the cgroup's css_sets list is in use if there are tasks

	   in the cpuset; the list is empty if there are none;

	   the cs->css.refcnt seems always 0 */

	if (list_empty(&cs->css.cgroup->css_sets))

		return;

	/*

	 * Find its next-highest non-empty parent, (top cpuset

	 * has online cpus, so can't be empty).

	 */

	parent = cs->parent;

	while (cpus_empty(parent->cpus_allowed)) {

		/*

		 * this empty cpuset should now be considered to

		 * have been used, and therefore eligible for

		 * release when empty (if it is notify_on_release)

		 */

		parent = parent->parent;

	}

	move_member_tasks_to_cpuset(cs, parent);

}

static void guarantee_online_cpus_mems_in_subtree(const struct cpuset *cur)

/*

 * Walk the specified cpuset subtree and look for empty cpusets.

 * The tasks of such cpuset must be moved to a parent cpuset.

 *

 * Note that such a notify_on_release cpuset must have had, at some time,

 * member tasks or cpuset descendants and cpus and memory, before it can

 * be a candidate for release.

 *

 * Called with manage_mutex held.  We take callback_mutex to modify

 * cpus_allowed and mems_allowed.

 *

 * This walk processes the tree from top to bottom, completing one layer

 * before dropping down to the next.  It always processes a node before

 * any of its children.

 *

 * For now, since we lack memory hot unplug, we'll never see a cpuset

 * that has tasks along with an empty 'mems'.  But if we did see such

 * a cpuset, we'd handle it just like we do if its 'cpus' was empty.

 */

static void scan_for_empty_cpusets(const struct cpuset *root)

{

	struct cpuset *cp;	/* scans cpusets being updated */

	struct cpuset *child;	/* scans child cpusets of cp */

	struct list_head queue;

	struct cgroup *cont;

	struct cpuset *c;

	/* Each of our child cpusets mems must be online */

	list_for_each_entry(cont, &cur->css.cgroup->children, sibling) {

		c = cgroup_cs(cont);

		guarantee_online_cpus_mems_in_subtree(c);

		if (!cpus_empty(c->cpus_allowed))

			guarantee_online_cpus(c, &c->cpus_allowed);

		if (!nodes_empty(c->mems_allowed))

			guarantee_online_mems(c, &c->mems_allowed);

	INIT_LIST_HEAD(&queue);

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

	mutex_lock(&callback_mutex);

	while (!list_empty(&queue)) {

		cp = container_of(queue.next, struct cpuset, stack_list);

		list_del(queue.next);

		list_for_each_entry(cont, &cp->css.cgroup->children, sibling) {

			child = cgroup_cs(cont);

			list_add_tail(&child->stack_list, &queue);

		}

		cont = cp->css.cgroup;

		/* Remove offline cpus and mems from this cpuset. */

		cpus_and(cp->cpus_allowed, cp->cpus_allowed, cpu_online_map);

		nodes_and(cp->mems_allowed, cp->mems_allowed,

						node_states[N_HIGH_MEMORY]);

		if ((cpus_empty(cp->cpus_allowed) ||

		     nodes_empty(cp->mems_allowed))) {

			/* Move tasks from the empty cpuset to a parent */

			mutex_unlock(&callback_mutex);

			remove_tasks_in_empty_cpuset(cp);

			mutex_lock(&callback_mutex);

		}

	}

	mutex_unlock(&callback_mutex);

	return;

}

/*

 * The cpus_allowed and mems_allowed nodemasks in the top_cpuset track

 * cpu_online_map and node_states[N_HIGH_MEMORY].  Force the top cpuset to

 * track what's online after any CPU or memory node hotplug or unplug

 * event.

 *

 * To ensure that we don't remove a CPU or node from the top cpuset

 * that is currently in use by a child cpuset (which would violate

 * the rule that cpusets must be subsets of their parent), we first

 * call the recursive routine guarantee_online_cpus_mems_in_subtree().

 * track what's online after any CPU or memory node hotplug or unplug event.

 *

 * Since there are two callers of this routine, one for CPU hotplug

 * events and one for memory node hotplug events, we could have coded

static void common_cpu_mem_hotplug_unplug(void)

{

	cgroup_lock();

	mutex_lock(&callback_mutex);

	guarantee_online_cpus_mems_in_subtree(&top_cpuset);

	top_cpuset.cpus_allowed = cpu_online_map;

	top_cpuset.mems_allowed = node_states[N_HIGH_MEMORY];

	scan_for_empty_cpusets(&top_cpuset);

	mutex_unlock(&callback_mutex);

	cgroup_unlock();

}