Roman Gushchin wrote: > On Fri, Jun 23, 2017 at 06:52:20AM +0900, Tetsuo Handa wrote: > > Tetsuo Handa wrote: > > 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(). > > That's interesting... Does it mean, that we have to give an access to the reserves > to all threads to guarantee the forward progress? Yes, for we don't have __GFP_KILLABLE flag. > > What do you think about Michal's approach? He posted a link in the thread. Please read that thread. -- 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
