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authorMichal Hocko <mhocko@suse.cz>2014-06-04 16:07:36 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-06-04 16:54:01 -0700
commitd8dc595ce3909fbc131bdf5ab8c9808fe624b18d (patch)
treed788c88fc3783e4b629a36b25b1da7f6b56aec41 /mm
parent675becce15f320337499bc1a9356260409a5ba29 (diff)
downloadlinux-d8dc595ce3909fbc131bdf5ab8c9808fe624b18d.tar.bz2
memcg: do not hang on OOM when killed by userspace OOM access to memory reserves
Eric has reported that he can see task(s) stuck in memcg OOM handler regularly. The only way out is to echo 0 > $GROUP/memory.oom_control His usecase is: - Setup a hierarchy with memory and the freezer (disable kernel oom and have a process watch for oom). - In that memory cgroup add a process with one thread per cpu. - In one thread slowly allocate once per second I think it is 16M of ram and mlock and dirty it (just to force the pages into ram and stay there). - When oom is achieved loop: * attempt to freeze all of the tasks. * if frozen send every task SIGKILL, unfreeze, remove the directory in cgroupfs. Eric has then pinpointed the issue to be memcg specific. All tasks are sitting on the memcg_oom_waitq when memcg oom is disabled. Those that have received fatal signal will bypass the charge and should continue on their way out. The tricky part is that the exit path might trigger a page fault (e.g. exit_robust_list), thus the memcg charge, while its memcg is still under OOM because nobody has released any charges yet. Unlike with the in-kernel OOM handler the exiting task doesn't get TIF_MEMDIE set so it doesn't shortcut further charges of the killed task and falls to the memcg OOM again without any way out of it as there are no fatal signals pending anymore. This patch fixes the issue by checking PF_EXITING early in mem_cgroup_try_charge and bypass the charge same as if it had fatal signal pending or TIF_MEMDIE set. Normally exiting tasks (aka not killed) will bypass the charge now but this should be OK as the task is leaving and will release memory and increasing the memory pressure just to release it in a moment seems dubious wasting of cycles. Besides that charges after exit_signals should be rare. I am bringing this patch again (rebased on the current mmotm tree). I hope we can move forward finally. If there is still an opposition then I would really appreciate a concurrent approach so that we can discuss alternatives. http://comments.gmane.org/gmane.linux.kernel.stable/77650 is a reference to the followup discussion when the patch has been dropped from the mmotm last time. Reported-by: Eric W. Biederman <ebiederm@xmission.com> Signed-off-by: Michal Hocko <mhocko@suse.cz> Acked-by: David Rientjes <rientjes@google.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/memcontrol.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c1b816f61536..9f4ff49c6add 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2684,7 +2684,8 @@ static int mem_cgroup_try_charge(struct mem_cgroup *memcg,
* free their memory.
*/
if (unlikely(test_thread_flag(TIF_MEMDIE) ||
- fatal_signal_pending(current)))
+ fatal_signal_pending(current) ||
+ current->flags & PF_EXITING))
goto bypass;
if (unlikely(task_in_memcg_oom(current)))