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

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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>
This commit is contained in:
Tejun Heo 2014-05-14 09:15:01 -04:00
parent 9e4173e1f2
commit 4e4e284723
1 changed files with 5 additions and 3 deletions
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8
kernel/cgroup.c
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@ -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);
}