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Commit 6f3d828f authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: remove cgroup->count and use 



cgroup->count tracks the number of css_sets associated with the cgroup
and used only to verify that no css_set is associated when the cgroup
is being destroyed.  It's superflous as the destruction path can
simply check whether cgroup->cset_links is empty instead.

Drop cgroup->count and check ->cset_links directly from
cgroup_destroy_locked().

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent ddd69148

include/linux/cgroup.h

+0 −6
Original line number Original line Diff line number Diff line
@@ -169,12 +169,6 @@ struct cgroup_name { 
struct cgroup {

struct cgroup {

	unsigned long flags;		/* "unsigned long" so bitops work */

	unsigned long flags;		/* "unsigned long" so bitops work */





	/*

	 * count users of this cgroup. >0 means busy, but doesn't

	 * necessarily indicate the number of tasks in the cgroup

	 */

	atomic_t count;



	int id;				/* ida allocated in-hierarchy ID */

	int id;				/* ida allocated in-hierarchy ID */





	/*

	/*

kernel/cgroup.c

+5 −16
Original line number Original line Diff line number Diff line
@@ -408,8 +408,7 @@ static void __put_css_set(struct css_set *cset, int taskexit) 
		list_del(&link->cgrp_link);

		list_del(&link->cgrp_link);





		/* @cgrp can't go away while we're holding css_set_lock */

		/* @cgrp can't go away while we're holding css_set_lock */

		if (atomic_dec_and_test(&cgrp->count) &&

		if (list_empty(&cgrp->cset_links) && notify_on_release(cgrp)) {

		    notify_on_release(cgrp)) {

			if (taskexit)

			if (taskexit)

				set_bit(CGRP_RELEASABLE, &cgrp->flags);

				set_bit(CGRP_RELEASABLE, &cgrp->flags);

			check_for_release(cgrp);

			check_for_release(cgrp);
@@ -616,7 +615,6 @@ static void link_css_set(struct list_head *tmp_links, struct css_set *cset, 
	link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link);

	link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link);

	link->cset = cset;

	link->cset = cset;

	link->cgrp = cgrp;

	link->cgrp = cgrp;

	atomic_inc(&cgrp->count);

	list_move(&link->cset_link, &cgrp->cset_links);

	list_move(&link->cset_link, &cgrp->cset_links);

	/*

	/*

	 * Always add links to the tail of the list so that the list

	 * Always add links to the tail of the list so that the list
@@ -4370,11 +4368,11 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) 
	lockdep_assert_held(&cgroup_mutex);

	lockdep_assert_held(&cgroup_mutex);





	/*

	/*

	 * css_set_lock prevents @cgrp from being removed while

	 * css_set_lock synchronizes access to ->cset_links and prevents

	 * __put_css_set() is in progress.

	 * @cgrp from being removed while __put_css_set() is in progress.

	 */

	 */

	read_lock(&css_set_lock);

	read_lock(&css_set_lock);

	empty = !atomic_read(&cgrp->count) && list_empty(&cgrp->children);

	empty = list_empty(&cgrp->cset_links) && list_empty(&cgrp->children);

	read_unlock(&css_set_lock);

	read_unlock(&css_set_lock);

	if (!empty)

	if (!empty)

		return -EBUSY;

		return -EBUSY;
@@ -5054,7 +5052,7 @@ void cgroup_exit(struct task_struct *tsk, int run_callbacks) 
static void check_for_release(struct cgroup *cgrp)

static void check_for_release(struct cgroup *cgrp)

{

{

	if (cgroup_is_releasable(cgrp) &&

	if (cgroup_is_releasable(cgrp) &&

	    !atomic_read(&cgrp->count) && list_empty(&cgrp->children)) {

	    list_empty(&cgrp->cset_links) && list_empty(&cgrp->children)) {

		/*

		/*

		 * Control Group is currently removeable. If it's not

		 * Control Group is currently removeable. If it's not

		 * already queued for a userspace notification, queue

		 * already queued for a userspace notification, queue
@@ -5422,11 +5420,6 @@ static void debug_css_free(struct cgroup *cont) 
	kfree(cont->subsys[debug_subsys_id]);

	kfree(cont->subsys[debug_subsys_id]);

}

}





static u64 cgroup_refcount_read(struct cgroup *cont, struct cftype *cft)

{

	return atomic_read(&cont->count);

}



static u64 debug_taskcount_read(struct cgroup *cont, struct cftype *cft)

static u64 debug_taskcount_read(struct cgroup *cont, struct cftype *cft)

{

{

	return cgroup_task_count(cont);

	return cgroup_task_count(cont);
@@ -5507,10 +5500,6 @@ static u64 releasable_read(struct cgroup *cgrp, struct cftype *cft) 
}

}





static struct cftype debug_files[] =  {

static struct cftype debug_files[] =  {

	{

		.name = "cgroup_refcount",

		.read_u64 = cgroup_refcount_read,

	},

	{

	{

		.name = "taskcount",

		.name = "taskcount",

		.read_u64 = debug_taskcount_read,

		.read_u64 = debug_taskcount_read,