On 2019/01/07 23:38, Michal Hocko wrote: > From: Michal Hocko <mhocko@xxxxxxxx> > > Tetsuo has reported [1] that a single process group memcg might easily > swamp the log with no-eligible oom victim reports due to race between > the memcg charge and oom_reaper This explanation is outdated. I reported that one memcg OOM killer can kill all processes in that memcg. I expect the changelog to be updated. > > Thread 1 Thread2 oom_reaper > try_charge try_charge > mem_cgroup_out_of_memory > mutex_lock(oom_lock) > mem_cgroup_out_of_memory > mutex_lock(oom_lock) > out_of_memory > select_bad_process > oom_kill_process(current) > wake_oom_reaper > oom_reap_task > MMF_OOM_SKIP->victim > mutex_unlock(oom_lock) > out_of_memory > select_bad_process # no task > > If Thread1 didn't race it would bail out from try_charge and force the > charge. We can achieve the same by checking tsk_is_oom_victim inside > the oom_lock and therefore close the race. > > [1] http://lkml.kernel.org/r/bb2074c0-34fe-8c2c-1c7d-db71338f1e7f@xxxxxxxxxxxxxxxxxxx > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx> > --- > mm/memcontrol.c | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index af7f18b32389..90eb2e2093e7 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1387,10 +1387,22 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask, > .gfp_mask = gfp_mask, > .order = order, > }; > - bool ret; > + bool ret = true; > > mutex_lock(&oom_lock); And because of "[PATCH 1/2] mm, oom: marks all killed tasks as oom victims", mark_oom_victim() will be called on current thread even if we used mutex_lock_killable(&oom_lock) here, like you said mutex_lock_killable would take care of exiting task already. I would then still prefer to check for mark_oom_victim because that is not racy with the exit path clearing signals. I can update my patch to use _killable lock variant if we are really going with the memcg specific fix. . If current thread is not yet killed by the OOM killer but can terminate without invoking the OOM killer, using mutex_lock_killable(&oom_lock) here saves some processes. What is the race you are referring by "racy with the exit path clearing signals" ? > + > + /* > + * multi-threaded tasks might race with oom_reaper and gain > + * MMF_OOM_SKIP before reaching out_of_memory which can lead > + * to out_of_memory failure if the task is the last one in > + * memcg which would be a false possitive failure reported > + */ Not only out_of_memory() failure. Current thread needlessly tries to select next OOM victim. out_of_memory() failure is nothing but a result of no eligible candidate case. > + if (tsk_is_oom_victim(current)) > + goto unlock; > + > ret = out_of_memory(&oc); > + > +unlock: > mutex_unlock(&oom_lock); > return ret; > } >
