Commit 1b51e65e authored Oct 07, 2016 by Michal Hocko Committed by Linus Torvalds Oct 07, 2016

oom, oom_reaper: allow to reap mm shared by the kthreads

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.

Link: http://lkml.kernel.org/r/1472119394-11342-10-git-send-email-mhocko@kernel.org


Signed-off-by: Michal Hocko <mhocko@suse.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 3f70dc38

mm/oom_kill.c

+7 −7

Original line number	Diff line number	Diff line
		@@ -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();

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