linux-kernel - Re: [PATCH] mm,oom: Exclude TIF_MEMDIE processes from candidates.

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Date:	Thu, 7 Jan 2016 15:58:41 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	rientjes@...gle.com, akpm@...ux-foundation.org, mgorman@...e.de,
	torvalds@...ux-foundation.org, oleg@...hat.com, hughd@...gle.com,
	andrea@...nel.org, riel@...hat.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm,oom: Exclude TIF_MEMDIE processes from candidates.

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;
 	}
-- 
Michal Hocko
SUSE Labs
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