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

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

[gregkh]

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 <stable@vger.kernel.org> know about it.


>From 33c35aa4817864e056fd772230b0c6b552e36ea2 Mon Sep 17 00:00:00 2001
From: Waiman Long <longman@redhat.com>
Date: Mon, 15 May 2017 09:34:06 -0400
Subject: cgroup: Prevent kill_css() from being called more than once

From: Waiman Long <longman@redhat.com>

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.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -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 */
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -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 longman@redhat.com are

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