Patch "cgroup: Prevent kill_css() from being called more than once" has been added to the 4.11-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.11-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
cgroup-prevent-kill_css-from-being-called-more-than-once.patch
and it can be found in the queue-4.11 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Waiman Long <[email protected]>
Date: Mon, 15 May 2017 09:34:06 -0400
Subject: cgroup: Prevent kill_css() from being called more than once

From: Waiman Long <[email protected]>

commit 33c35aa4817864e056fd772230b0c6b552e36ea2 upstream.

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.

---
 include/linux/cgroup-defs.h |    1 +
 kernel/cgroup/cgroup.c      |    5 +++++
 2 files changed, 6 insertions(+)

@@ -47,6 +47,7 @@ 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 */

@@ -4265,6 +4265,11 @@ static void kill_css(struct cgroup_subsy
 {
 	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.

Patches currently in stable-queue which might be from [email protected] are

queue-4.11/cgroup-prevent-kill_css-from-being-called-more-than-once.patch