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authorAnton Vorontsov <anton.vorontsov@linaro.org>2012-02-24 05:14:46 +0400
committerLinus Torvalds <torvalds@linux-foundation.org>2012-02-24 08:55:51 -0800
commit371528caec553785c37f73fa3926ea0de84f986f (patch)
treecc718011d32ae17ec61d1a68b71f912caf26b5bb /mm
parent37fbf4bfb826372c3ca6c09d8a015d1fe9f5e186 (diff)
downloadlinux-371528caec553785c37f73fa3926ea0de84f986f.tar.gz
mm: memcg: Correct unregistring of events attached to the same eventfd
There is an issue when memcg unregisters events that were attached to the same eventfd: - On the first call mem_cgroup_usage_unregister_event() removes all events attached to a given eventfd, and if there were no events left, thresholds->primary would become NULL; - Since there were several events registered, cgroups core will call mem_cgroup_usage_unregister_event() again, but now kernel will oops, as the function doesn't expect that threshold->primary may be NULL. That's a good question whether mem_cgroup_usage_unregister_event() should actually remove all events in one go, but nowadays it can't do any better as cftype->unregister_event callback doesn't pass any private event-associated cookie. So, let's fix the issue by simply checking for threshold->primary. FWIW, w/o the patch the following oops may be observed: BUG: unable to handle kernel NULL pointer dereference at 0000000000000004 IP: [<ffffffff810be32c>] mem_cgroup_usage_unregister_event+0x9c/0x1f0 Pid: 574, comm: kworker/0:2 Not tainted 3.3.0-rc4+ #9 Bochs Bochs RIP: 0010:[<ffffffff810be32c>] [<ffffffff810be32c>] mem_cgroup_usage_unregister_event+0x9c/0x1f0 RSP: 0018:ffff88001d0b9d60 EFLAGS: 00010246 Process kworker/0:2 (pid: 574, threadinfo ffff88001d0b8000, task ffff88001de91cc0) Call Trace: [<ffffffff8107092b>] cgroup_event_remove+0x2b/0x60 [<ffffffff8103db94>] process_one_work+0x174/0x450 [<ffffffff8103e413>] worker_thread+0x123/0x2d0 Cc: stable <stable@vger.kernel.org> Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: Michal Hocko <mhocko@suse.cz> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/memcontrol.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 6728a7ae6f2..228d6461c12 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4414,6 +4414,9 @@ static void mem_cgroup_usage_unregister_event(struct cgroup *cgrp,
*/
BUG_ON(!thresholds);
+ if (!thresholds->primary)
+ goto unlock;
+
usage = mem_cgroup_usage(memcg, type == _MEMSWAP);
/* Check if a threshold crossed before removing */
@@ -4462,7 +4465,7 @@ swap_buffers:
/* To be sure that nobody uses thresholds */
synchronize_rcu();
-
+unlock:
mutex_unlock(&memcg->thresholds_lock);
}