3.0-stable review patch. If anyone has any objections, please let me know.
------------------ From: Anton Vorontsov <[email protected]> commit 371528caec553785c37f73fa3926ea0de84f986f upstream. 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 Signed-off-by: Anton Vorontsov <[email protected]> Acked-by: KAMEZAWA Hiroyuki <[email protected]> Cc: Kirill A. Shutemov <[email protected]> Cc: Michal Hocko <[email protected]> Signed-off-by: Linus Torvalds <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- mm/memcontrol.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -4558,6 +4558,9 @@ static void mem_cgroup_usage_unregister_ */ BUG_ON(!thresholds); + if (!thresholds->primary) + goto unlock; + usage = mem_cgroup_usage(memcg, type == _MEMSWAP); /* Check if a threshold crossed before removing */ @@ -4606,7 +4609,7 @@ swap_buffers: /* To be sure that nobody uses thresholds */ synchronize_rcu(); - +unlock: mutex_unlock(&memcg->thresholds_lock); } -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
