Michal Hocko wrote:

quoted

quoted

Anyway, would you be OK with the patch if I added the current->mm check
and resolve its necessity in a separate patch?

Please correct task_will_free_mem() in oom_kill_process() as well.

We cannot hold task_lock over all task_will_free_mem I am even not sure
we have to develop an elaborate way to make it raceless just for the nommu
case. The current case is simple as we cannot race here. Is that
sufficient for you?

We can use find_lock_task_mm() inside mark_oom_victim().
That is, call wake_oom_reaper() from mark_oom_victim() like

void mark_oom_victim(struct task_struct *tsk, bool can_use_oom_reaper)
{
	WARN_ON(oom_killer_disabled);
	/* OOM killer might race with memcg OOM */
	tsk = find_lock_task_mm(tsk);
	if (!tsk)
		return;
	if (test_and_set_tsk_thread_flag(tsk, TIF_MEMDIE)) {
		task_unlock(tsk);
		return;
	}
	task_unlock(tsk);
	atomic_inc(&tsk->signal->oom_victims);
	/*
	 * Make sure that the task is woken up from uninterruptible sleep
	 * if it is frozen because OOM killer wouldn't be able to free
	 * any memory and livelock. freezing_slow_path will tell the freezer
	 * that TIF_MEMDIE tasks should be ignored.
	 */
	__thaw_task(tsk);
	atomic_inc(&oom_victims);
	if (can_use_oom_reaper)
		wake_oom_reaper(tsk);
}

and move mark_oom_victim() by normal path to after task_unlock(victim).

 	do_send_sig_info(SIGKILL, SEND_SIG_FORCED, victim, true);
-	mark_oom_victim(victim);

-	if (can_oom_reap)
-		wake_oom_reaper(victim);
+	wake_oom_reaper(victim, can_oom_reap);

If you don't like possibility of showing different pid for

	pr_err("Killed process %d (%s)

and

	pr_info("oom_reaper: reaped process %d (%s)

messages, you can defer the former till mark_oom_victim() locks that task.

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