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authorMartijn Coenen <maco@google.com>2016-01-15 16:57:49 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2016-01-15 17:56:32 -0800
commit6611d8d76132f86faa501de9451a89bf23fb2371 (patch)
tree3f1972adb32677c3e000db5f9c3dcbf06bb140f0
parent98fd1ef4241ce0c700a174dd3e33c643b4774690 (diff)
memcg: only free spare array when readers are done
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> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/memcontrol.c11
1 files changed, 6 insertions, 5 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 23d8cf5a86c3..0eda67376df4 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3491,16 +3491,17 @@ 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);
}