@@ -5602,16 +5602,17 @@ static void __mem_cgroup_usage_unregister_event(struct mem_cgroup *memcg,
swap_buffers:
/* Swap primary and spare array */
thresholds->spare = thresholds->primary;
- /* If all events are unregistered, free the spare array */
- if (!new) {
- kfree(thresholds->spare);
- thresholds->spare = NULL;
- }
rcu_assign_pointer(thresholds->primary, new);
/* To be sure that nobody uses thresholds */
synchronize_rcu();
+
+ /* If all events are unregistered, free the spare array */
+ if (!new) {
+ kfree(thresholds->spare);
+ thresholds->spare = NULL;
+ }
unlock:
mutex_unlock(&memcg->thresholds_lock);
}
This is a note to let you know that I have just added a patch titled memcg: only free spare array when readers are done to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree which can be found at: http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue This patch is scheduled to be released in version 3.16.7-ckt24. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.16.y-ckt tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Luis ---8<------------------------------------------------------------ From b3bcee19d0aadcc9ab183303775b261b3c354f1f Mon Sep 17 00:00:00 2001 From: Martijn Coenen <maco@google.com> Date: Fri, 15 Jan 2016 16:57:49 -0800 Subject: memcg: only free spare array when readers are done commit 6611d8d76132f86faa501de9451a89bf23fb2371 upstream. A spare array holding mem cgroup threshold events is kept around to make sure we can always safely deregister an event and have an array to store the new set of events in. In the scenario where we're going from 1 to 0 registered events, the pointer to the primary array containing 1 event is copied to the spare slot, and then the spare slot is freed because no events are left. However, it is freed before calling synchronize_rcu(), which means readers may still be accessing threshold->primary after it is freed. Fixed by only freeing after synchronize_rcu(). Signed-off-by: Martijn Coenen <maco@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Michal Hocko <mhocko@suse.com> Cc: Vladimir Davydov <vdavydov@virtuozzo.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- mm/memcontrol.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-)