On 2018/10/22 16:13, 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 > > 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 e79cb59552d9..a9dfed29967b 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1380,10 +1380,22 @@ 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); > + > + /* > + * 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 > + */ > + if (tsk_is_oom_victim(current)) > + goto unlock; > + This is not wrong but is strange. We can use mutex_lock_killable(&oom_lock) so that any killed threads no longer wait for oom_lock. Also, closing this race for only memcg OOM path is strange. Global OOM path (which are CLONE_VM without CLONE_THREAD) is still suffering this race (though frequency is lower than memcg OOM due to use of mutex_trylock()). Either checking before calling out_of_memory() or checking task_will_free_mem(current) inside out_of_memory() will close this race for both paths. > ret = out_of_memory(&oc); > + > +unlock: > mutex_unlock(&oom_lock); > return ret; > } >
