On Sun 04-09-16 10:49:52, Tetsuo Handa wrote: > Michal Hocko wrote: > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index 9ee178ba7b71..df58733ca48e 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -1899,7 +1899,7 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask, > > * bypass the last charges so that they can exit quickly and > > * free their memory. > > */ > > - if (unlikely(test_thread_flag(TIF_MEMDIE) || > > + if (unlikely(tsk_is_oom_victim(current) || > > fatal_signal_pending(current) || > > current->flags & PF_EXITING)) > > goto force; > > Does this test_thread_flag(TIF_MEMDIE) (or tsk_is_oom_victim(current)) make sense? > > If current thread is OOM-killed, SIGKILL must be pending before arriving at > do_exit() and PF_EXITING must be set after arriving at do_exit(). But I can't > find locations which do memory allocation between clearing SIGKILL and setting > PF_EXITING. > > When can test_thread_flag(TIF_MEMDIE) == T (or tsk_is_oom_victim(current) == T) && > fatal_signal_pending(current) == F && (current->flags & PF_EXITING) == 0 happen? Maybe you are right. I would have to double check. I am still drown in a pile of emails after vacation so it will take some time to do that. Anyway I believe this would be worth a separate patch. This one just mechanically replaces TIF_MEMDIE check by tsk_is_oom_victim. > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > > index b11977585c7b..e26529edcee3 100644 > > --- a/mm/oom_kill.c > > +++ b/mm/oom_kill.c > > @@ -1078,7 +1078,7 @@ void pagefault_out_of_memory(void) > > * be a racing OOM victim for which oom_killer_disable() > > * is waiting for. > > */ > > - WARN_ON(test_thread_flag(TIF_MEMDIE)); > > + WARN_ON(tsk_is_oom_victim(current)); > > } > > > > mutex_unlock(&oom_lock); > > Does this WARN_ON() make sense? > > When some user thread called oom_killer_disable(), there are running > kernel threads but is no running user threads except the one which > called oom_killer_disable(). Since oom_killer_disable() waits for > oom_lock, out_of_memory() called from here shall not return false > before oom_killer_disable() sets oom_killer_disabled = true. Thus, > possible situation out_of_memory() called from here can return false > are limited to > > (a) the one which triggered pagefaults after returning from > oom_killer_disable() > (b) An OOM victim which was thawed triggered pagefaults from do_exit() > after the one which called oom_killer_disable() released oom_lock > (c) kernel threads which triggered pagefaults after use_mm() > > . And since kernel threads are not subjected to mark_oom_victim(), > test_thread_flag(TIF_MEMDIE) == F (or tsk_is_oom_victim(current) == F) > for kernel threads. Thus, possible situation out_of_memory() called from > here can return false and we hit this WARN_ON() is limited to (b). > > Even if (a) or (b) is possible, does continuously emitting backtraces > help? It seems to me that the system is under OOM livelock situation and > we need to take a different action (e.g. try to allocate a page using > ALLOC_NO_WATERMARKS in order to make the pagefault be solved, and panic() > if failed) than emitting same backtraces forever. I have to think about this some more, so I cannot give it any answer right now. But again, this is just a mechanical change. If your concern is correct and the WARN_ON is really pointless it should be similarly pointless with the TIF_MEMDIE check unless I am missing something. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>