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cgroup: Prevent kill_css() from being called more than once

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The kill_css() function may be called more than once under the condition
that the css was killed but not physically removed yet followed by the
removal of the cgroup that is hosting the css. This patch prevents any
harmm from being done when that happens.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: stable@vger.kernel.org # v4.5+
This commit is contained in:
Waiman Long 2017-05-15 09:34:06 -04:00 committed by Tejun Heo
parent 2ea659a9ef
commit 33c35aa481
2 changed files with 6 additions and 0 deletions
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1
include/linux/cgroup-defs.h
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@ -48,6 +48,7 @@ enum {
CSS_ONLINE = (1 << 1), /* between ->css_online() and ->css_offline() */
CSS_RELEASED = (1 << 2), /* refcnt reached zero, released */
CSS_VISIBLE = (1 << 3), /* css is visible to userland */
CSS_DYING = (1 << 4), /* css is dying */
};
/* bits in struct cgroup flags field */

5
kernel/cgroup/cgroup.c
View file

@ -4265,6 +4265,11 @@ static void kill_css(struct cgroup_subsys_state *css)
{
lockdep_assert_held(&cgroup_mutex);
if (css->flags & CSS_DYING)
return;
css->flags |= CSS_DYING;
/*
* This must happen before css is disassociated with its cgroup.
* See seq_css() for details.