On Thu 07-01-16 15:58:41, Michal Hocko wrote:
> On Thu 07-01-16 22:31:32, Tetsuo Handa wrote:
> [...]
> > I think we need to filter at select_bad_process() and oom_kill_process().
> >
> > When P has no children, P is chosen and TIF_MEMDIE is set on P. But P can
> > be chosen forever due to P->signal->oom_score_adj == OOM_SCORE_ADJ_MAX
> > even if the OOM reaper reclaimed P's mm. We need to ensure that
> > oom_kill_process() is not called with P if P already has TIF_MEMDIE.
>
> Hmm. Any task is allowed to set its oom_score_adj that way and I
> guess we should really make sure that at least sysrq+f will make some
> progress. This is what I would do. Again I think this is worth a
> separate patch. Unless there are any objections I will roll out what I
> have and post 3 separate patches.
> ---
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 45e51ad2f7cf..ee34a51bd65a 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -333,6 +333,14 @@ static struct task_struct *select_bad_process(struct oom_control *oc,
> if (points == chosen_points && thread_group_leader(chosen))
> continue;
>
> + /*
> + * If the current major task is already ooom killed and this
> + * is sysrq+f request then we rather choose somebody else
> + * because the current oom victim might be stuck.
> + */
> + if (is_sysrq_oom(sc) && test_tsk_thread_flag(p, TIF_MEMDIE))
> + continue;
> +
> chosen = p;
> chosen_points = points;
> }
I guess we can move this up to oom_scan_process_thread already. It would
be simpler and I it should be also more appropriate because we already
do sysrq specific handling there:
---
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 45e51ad2f7cf..a27a43212075 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -277,10 +277,16 @@ enum oom_scan_t oom_scan_process_thread(struct oom_control *oc,
/*
* This task already has access to memory reserves and is being killed.
* Don't allow any other task to have access to the reserves.
+ * If we are doing sysrq+f then it doesn't make any sense to check such
+ * a task because it might be stuck and unable to terminate while the
+ * forced OOM might be the only option left to get the system back to
+ * work.
*/
if (test_tsk_thread_flag(task, TIF_MEMDIE)) {
if (!is_sysrq_oom(oc))
return OOM_SCAN_ABORT;
+ else
+ return OOM_SCAN_CONTINUE;
}
if (!task->mm)
return OOM_SCAN_CONTINUE;
--
Michal Hocko
SUSE Labs
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