On Fri 24-06-16 20:02:01, Tetsuo Handa wrote: > Currently, the OOM reaper calls exit_oom_victim() on remote TIF_MEMDIE > thread after an OOM reap attempt was made. This behavior is intended > for allowing oom_scan_process_thread() to select next OOM victim by > making atomic_read(&task->signal->oom_victims) == 0. > > But since threads can be blocked for unbounded period at __mmput() from > mmput() from exit_mm() from do_exit(), we can't risk the OOM reaper > being blocked for unbounded period waiting for TIF_MEMDIE threads. > Therefore, when we hit a situation that a TIF_MEMDIE thread which is > the only thread of that thread group reached tsk->mm = NULL line in > exit_mm() from do_exit() before __oom_reap_task() finds a mm via > find_lock_task_mm(), oom_reap_task() does not wait for the TIF_MEMDIE > thread to return from __mmput() and instead calls exit_oom_victim(). > > Patch "mm, oom: hide mm which is shared with kthread or global init" > tried to avoid OOM livelock by setting MMF_OOM_REAPED, but it is racy > because setting MMF_OOM_REAPED will not help when find_lock_task_mm() > in oom_scan_process_thread() failed. I haven't thought that through yet (I will wait for the monday fresh brain) but wouldn't the following be sufficient? --- diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 4c21f744daa6..72360d7284a6 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -295,7 +295,8 @@ enum oom_scan_t oom_scan_process_thread(struct oom_control *oc, if (test_bit(MMF_OOM_REAPED, &p->mm->flags)) ret = OOM_SCAN_CONTINUE; task_unlock(p); - } + } else if (task->state == EXIT_ZOMBIE) + ret = OOM_SCAN_CONTINUE; return ret; } @@ -592,14 +593,7 @@ static void oom_reap_task(struct task_struct *tsk) debug_show_all_locks(); } - /* - * Clear TIF_MEMDIE because the task shouldn't be sitting on a - * reasonably reclaimable memory anymore or it is not a good candidate - * for the oom victim right now because it cannot release its memory - * itself nor by the oom reaper. - */ tsk->oom_reaper_list = NULL; - exit_oom_victim(tsk); /* Drop a reference taken by wake_oom_reaper */ put_task_struct(tsk); -- 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>