cgroup: Prevent kill_css() from being called more than once
authorWaiman Long <longman@redhat.com>
Mon, 15 May 2017 13:34:06 +0000 (09:34 -0400)
committerTejun Heo <tj@kernel.org>
Wed, 17 May 2017 20:58:32 +0000 (16:58 -0400)
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+
include/linux/cgroup-defs.h
kernel/cgroup/cgroup.c

index 2174594..ec47101 100644 (file)
@@ -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 */
index c3c9a0e..8d4e85e 100644 (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.