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authorMartijn Coenen <maco@google.com>2016-01-15 16:57:49 -0800
committerJiri Slaby <jslaby@suse.cz>2016-02-25 10:49:15 +0100
commit1c2456e301b60e027413bc4aec797a343a2b0d50 (patch)
tree8f71de1e221bd41ff9884db6b0a652f723570994
parent72ecf7ea4ad85bc9b0ce90f34c8c08f628d6be8b (diff)
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: Jiri Slaby <jslaby@suse.cz>
-rw-r--r--mm/memcontrol.c11
1 files changed, 6 insertions, 5 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ff648969e402..5904fc833523 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5830,16 +5830,17 @@ static void mem_cgroup_usage_unregister_event(struct cgroup_subsys_state *css,
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);
}