Tetsuo Handa wrote: > Roman Gushchin wrote: > > On Thu, Jun 22, 2017 at 09:40:28AM +0900, Tetsuo Handa wrote: > > > Roman Gushchin wrote: > > > > --- a/mm/oom_kill.c > > > > +++ b/mm/oom_kill.c > > > > @@ -992,6 +992,13 @@ bool out_of_memory(struct oom_control *oc) > > > > if (oom_killer_disabled) > > > > return false; > > > > > > > > + /* > > > > + * If there are oom victims in flight, we don't need to select > > > > + * a new victim. > > > > + */ > > > > + if (atomic_read(&oom_victims) > 0) > > > > + return true; > > > > + > > > > if (!is_memcg_oom(oc)) { > > > > blocking_notifier_call_chain(&oom_notify_list, 0, &freed); > > > > if (freed > 0) > > > > > > The OOM reaper is not available for CONFIG_MMU=n kernels, and timeout based > > > giveup is not permitted, but a multithreaded process might be selected as > > > an OOM victim. Not setting TIF_MEMDIE to all threads sharing an OOM victim's > > > mm increases possibility of preventing some OOM victim thread from terminating > > > (e.g. one of them cannot leave __alloc_pages_slowpath() with mmap_sem held for > > > write due to waiting for the TIF_MEMDIE thread to call exit_oom_victim() when > > > the TIF_MEMDIE thread is waiting for the thread with mmap_sem held for write). > > > > I agree, that CONFIG_MMU=n is a special case, and the proposed approach can't > > be used directly. But can you, please, why do you find the first chunk wrong? > > Since you are checking oom_victims before checking task_will_free_mem(current), > only one thread can get TIF_MEMDIE. This is where a multithreaded OOM victim without > the OOM reaper can get stuck forever. Oops, I misinterpreted. This is where a multithreaded OOM victim with or without the OOM reaper can get stuck forever. Think about a process with two threads is selected by the OOM killer and only one of these two threads can get TIF_MEMDIE. Thread-1 Thread-2 The OOM killer The OOM reaper Calls down_write(¤t->mm->mmap_sem). Enters __alloc_pages_slowpath(). Enters __alloc_pages_slowpath(). Takes oom_lock. Calls out_of_memory(). Selects Thread-1 as an OOM victim. Gets SIGKILL. Gets SIGKILL. Gets TIF_MEMDIE. Releases oom_lock. Leaves __alloc_pages_slowpath() because Thread-1 has TIF_MEMDIE. Takes oom_lock. Will do nothing because down_read_trylock() fails. Releases oom_lock. Gives up and sets MMF_OOM_SKIP after one second. Takes oom_lock. Calls out_of_memory(). Will not check MMF_OOM_SKIP because Thread-1 still has TIF_MEMDIE. // <= get stuck waiting for Thread-1. Releases oom_lock. Will not leave __alloc_pages_slowpath() because Thread-2 does not have TIF_MEMDIE. Will not call up_write(¤t->mm->mmap_sem). Reaches do_exit(). Calls down_read(¤t->mm->mmap_sem) in exit_mm() in do_exit(). // <= get stuck waiting for Thread-2. Will not call up_read(¤t->mm->mmap_sem) in exit_mm() in do_exit(). Will not clear TIF_MEMDIE in exit_oom_victim() in exit_mm() in do_exit(). -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html