linux-kernel - [PATCH 06/10] mm, oom: kill all tasks sharing the mm

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Message-Id: <1466426628-15074-7-git-send-email-mhocko@kernel.org>
Date:	Mon, 20 Jun 2016 14:43:44 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	<linux-mm@...ck.org>
Cc:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	David Rientjes <rientjes@...gle.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...e.com>
Subject: [PATCH 06/10] mm, oom: kill all tasks sharing the mm

From: Michal Hocko <mhocko@...e.com>

Currently oom_kill_process skips both the oom reaper and SIG_KILL if a
process sharing the same mm is unkillable via OOM_ADJUST_MIN. After "mm,
oom_adj: make sure processes sharing mm have same view of oom_score_adj"
all such processes are sharing the same value so we shouldn't see such a
task at all (oom_badness would rule them out).

We can still encounter oom disabled vforked task which has to be killed
as well if we want to have other tasks sharing the mm reapable
because it can access the memory before doing exec. Killing such a task
should be acceptable because it is highly unlikely it has done anything
useful because it cannot modify any memory before it calls exec. An
alternative would be to keep the task alive and skip the oom reaper and
risk all the weird corner cases where the OOM killer cannot make forward
progress because the oom victim hung somewhere on the way to exit.

[rientjes@...gle.com - drop printk when OOM_SCORE_ADJ_MIN killed task
 the setting is inherently racy and we cannot do much about it without
 introducing locks in hot paths]
Acked-by: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: Michal Hocko <mhocko@...e.com>
---
 mm/oom_kill.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 02da660b7c25..38f89ac2df7f 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -852,8 +852,7 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
 			continue;
 		if (same_thread_group(p, victim))
 			continue;
-		if (unlikely(p->flags & PF_KTHREAD) || is_global_init(p) ||
-		    p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {
+		if (unlikely(p->flags & PF_KTHREAD) || is_global_init(p)) {
 			/*
 			 * We cannot use oom_reaper for the mm shared by this
 			 * process because it wouldn't get killed and so the
-- 
2.8.1