Michal Hocko wrote:
> On Fri 24-06-16 01:24:46, Tetsuo Handa wrote:
> > I missed that victim != p case needs to use get_task_struct(). Patch updated.
> > ----------------------------------------
> > >From 1819ec63b27df2d544f66482439e754d084cebed Mon Sep 17 00:00:00 2001
> > From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> > Date: Fri, 24 Jun 2016 01:16:02 +0900
> > Subject: [PATCH v2] mm, oom: don't set TIF_MEMDIE on a mm-less thread.
> >
> > Patch "mm, oom: fortify task_will_free_mem" removed p->mm != NULL test for
> > shortcut path in oom_kill_process(). But since commit f44666b04605d1c7
> > ("mm,oom: speed up select_bad_process() loop") changed to iterate using
> > thread group leaders, the possibility of p->mm == NULL has increased
> > compared to when commit 83363b917a2982dd ("oom: make sure that TIF_MEMDIE
> > is set under task_lock") was proposed. On CONFIG_MMU=n kernels, nothing
> > will clear TIF_MEMDIE and the system can OOM livelock if TIF_MEMDIE was
> > by error set to a mm-less thread group leader.
> >
> > Let's do steps for regular path except printing OOM killer messages and
> > sending SIGKILL.
>
> I fully agree with Oleg. It would be much better to encapsulate this
> into mark_oom_victim and guard it by ifdef NOMMU as this is nommu
> specific with a big fat warning why we need it.
OK. But before doing so, which one ((A) or (B) shown below) do you prefer?
(A) Don't use task_will_free_mem(p) shortcut in oom_kill_process() if CONFIG_MMU=n.
Since task_will_free_mem(p) == true where p is the largest memory consumer
(with oom_score_adj taken into account) is not exiting smoothly, as with
commit 6a618957ad17d8f4 ("mm: oom_kill: don't ignore oom score on exiting
tasks") thought, it can be a sign of something bad (possibly OOM livelock) is
happening. Thus, print the OOM killer messages anyway although all tasks
which will be OOM killed are already killed/exiting (unless p has OOM killable
children). This will help giving administrator a hint when the kernel hit
OOM livelock.
----------
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 4c21f74..e7d38f62 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -834,6 +834,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
DEFAULT_RATELIMIT_BURST);
bool can_oom_reap = true;
+#ifdef CONFIG_MMU
/*
* If the task is already exiting, don't alarm the sysadmin or kill
* its children or threads, just set TIF_MEMDIE so it can die quickly
@@ -844,6 +845,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
put_task_struct(p);
return;
}
+#endif
if (__ratelimit(&oom_rs))
dump_header(oc, p);
----------
(B) Check mm in mark_oom_victim() if CONFIG_MMU=n.
Since mark_oom_victim() is also called from current->mm && task_will_free_mem(current)
shortcut in out_of_memory(), mark_oom_victim(current) needs to set TIF_MEMDIE on current
if current->mm != NULL.
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 4c21f74..bf45666 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -668,9 +668,29 @@ subsys_initcall(oom_init)
void mark_oom_victim(struct task_struct *tsk)
{
WARN_ON(oom_killer_disabled);
+#ifdef CONFIG_MMU
/* OOM killer might race with memcg OOM */
if (test_and_set_tsk_thread_flag(tsk, TIF_MEMDIE))
return;
+#else
+ /*
+ * Make sure that we set TIF_MEMDIE on a thread with mm in order to
+ * reduce possibility of hitting OOM livelock.
+ */
+ task_lock(tsk);
+ if (!tsk->mm) {
+ task_unlock(tsk);
+ tsk = find_lock_task_mm(tsk);
+ if (!tsk)
+ return;
+ }
+ /* OOM killer might race with memcg OOM */
+ if (test_and_set_tsk_thread_flag(tsk, TIF_MEMDIE)) {
+ task_unlock(tsk);
+ return;
+ }
+ task_unlock(tsk);
+#endif
atomic_inc(&tsk->signal->oom_victims);
/*
* Make sure that the task is woken up from uninterruptible sleep
--
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>