On Sat 22-07-17 00:18:48, Tetsuo Handa wrote: > Michal Hocko wrote: > > > If we ignore MMF_OOM_SKIP once, we can avoid sequence above. > > > > But we set MMF_OOM_SKIP _after_ the process lost its address space (well > > after the patch which allows to race oom reaper with the exit_mmap). > > > > > > > > Process-1 Process-2 > > > > > > Takes oom_lock. > > > Fails get_page_from_freelist(). > > > Enters out_of_memory(). > > > Get SIGKILL. > > > Get TIF_MEMDIE. > > > Leaves out_of_memory(). > > > Releases oom_lock. > > > Enters do_exit(). > > > Calls __mmput(). > > > Takes oom_lock. > > > Fails get_page_from_freelist(). > > > Releases some memory. > > > Sets MMF_OOM_SKIP. > > > Enters out_of_memory(). > > > Ignores MMF_OOM_SKIP mm once. > > > Leaves out_of_memory(). > > > Releases oom_lock. > > > Succeeds get_page_from_freelist(). > > > > OK, so let's say you have another task just about to jump into > > out_of_memory and ... end up in the same situation. > > Right. > > > > > This race is just > > unavoidable. > > There is no perfect way (always timing dependent). But I would rather not add a code which _pretends_ it solves something. If we see the above race a real problem in out there then we should think about how to fix it. I definitely do not want to add more hack into an already complicated code base. -- 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>
