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From: Michal Hocko <mhocko@kernel.org>
To: linux-mm@kvack.org
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
	Oleg Nesterov <oleg@redhat.com>,
	David Rientjes <rientjes@google.com>,
	Vladimir Davydov <vdavydov@parallels.com>,
	Michal Hocko <mhocko@suse.com>
Subject: [PATCH v2 9/9] oom, oom_reaper: allow to reap mm shared by the kthreads
Date: Thu, 25 Aug 2016 12:03:14 +0200
Message-ID: <1472119394-11342-10-git-send-email-mhocko@kernel.org> (raw)
In-Reply-To: <1472119394-11342-1-git-send-email-mhocko@kernel.org>

From: Michal Hocko <mhocko@suse.com>

oom reaper was skipped for an mm which is shared with the kernel thread
(aka use_mm()). The primary concern was that such a kthread might want
to read from the userspace memory and see zero page as a result of the
oom reaper action. This is no longer a problem after "mm: make sure that
kthreads will not refault oom reaped memory" because any attempt to
fault in when the MMF_UNSTABLE is set will result in SIGBUS and so the
target user should see an error. This means that we can finally allow
oom reaper also to tasks which share their mm with kthreads.

Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 mm/oom_kill.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 5a3ba96c8338..10f686969fc4 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -902,13 +902,7 @@ static void oom_kill_process(struct oom_control *oc, const char *message)
 			continue;
 		if (same_thread_group(p, victim))
 			continue;
-		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
-			 * memory might be still used. Hide the mm from the oom
-			 * killer to guarantee OOM forward progress.
-			 */
+		if (is_global_init(p)) {
 			can_oom_reap = false;
 			set_bit(MMF_OOM_SKIP, &mm->flags);
 			pr_info("oom killer %d (%s) has mm pinned by %d (%s)\n",
@@ -916,6 +910,12 @@ static void oom_kill_process(struct oom_control *oc, const char *message)
 					task_pid_nr(p), p->comm);
 			continue;
 		}
+		/*
+		 * No use_mm() user needs to read from the userspace so we are
+		 * ok to reap it.
+		 */
+		if (unlikely(p->flags & PF_KTHREAD))
+			continue;
 		do_send_sig_info(SIGKILL, SEND_SIG_FORCED, p, true);
 	}
 	rcu_read_unlock();
-- 
2.8.1

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      parent reply index

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-08-25 10:03 [PATCH v2 0/10] fortify oom killer even more Michal Hocko
2016-08-25 10:03 ` [PATCH v2 1/9] mm,oom_reaper: Reduce find_lock_task_mm() usage Michal Hocko
2016-08-25 10:03 ` [PATCH v2 2/9] mm,oom_reaper: Do not attempt to reap a task twice Michal Hocko
2016-08-25 10:03 ` [PATCH v2 3/9] oom: keep mm of the killed task available Michal Hocko
2016-08-25 10:03 ` [PATCH v2 4/9] kernel, oom: fix potential pgd_lock deadlock from __mmdrop Michal Hocko
2016-08-25 10:03 ` [PATCH v2 5/9] mm, oom: get rid of signal_struct::oom_victims Michal Hocko
2016-08-25 10:03 ` [PATCH v2 6/9] oom, suspend: fix oom_killer_disable vs. pm suspend properly Michal Hocko
2016-08-25 10:03 ` [PATCH v2 7/9] mm, oom: enforce exit_oom_victim on current task Michal Hocko
2016-08-25 10:03 ` [PATCH v2 8/9] mm: make sure that kthreads will not refault oom reaped memory Michal Hocko
2016-08-25 10:03 ` Michal Hocko [this message]

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