Commit 4e4e2847 authored May 14, 2014 by Tejun Heo

cgroup: move cgroup->sibling unlinking to cgroup_put()

Move cgroup->sibling unlinking from cgroup_destroy_css_killed() to
cgroup_put(). This is later but still before the RCU grace period, so
it doesn't break css_next_child() although there now is a larger
window in which a dead cgroup is visible during css iteration. As css
iteration always could have included offline csses, this doesn't
affect correctness; however, it does make css_next_child() fall back
to reiterting mode more often. This also makes cgroup_put() directly
take cgroup_mutex, which limits where it can be called from. These
are not immediately problematic and will be dealt with later.

This change enables simplification of cgroup destruction path.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>

parent 9e4173e1

kernel/cgroup.c

+5 −3

Original line number	Diff line number	Diff line
		@@ -1056,6 +1056,11 @@ static void cgroup_put(struct cgroup *cgrp)
		if (WARN_ON_ONCE(cgrp->parent && !cgroup_is_dead(cgrp)))
		return;

		/* delete this cgroup from parent->children */
		mutex_lock(&cgroup_mutex);
		list_del_rcu(&cgrp->sibling);
		mutex_unlock(&cgroup_mutex);

		cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
		cgrp->id = -1;

		@@ -4561,9 +4566,6 @@ static void cgroup_destroy_css_killed(struct cgroup *cgrp)
		{
		lockdep_assert_held(&cgroup_mutex);

		/* delete this cgroup from parent->children */
		list_del_rcu(&cgrp->sibling);

		cgroup_put(cgrp);
		}

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