Commit cbdcf7f7 authored Jun 03, 2016 by Michal Hocko Committed by Linus Torvalds Jun 03, 2016

mm, oom_reaper: do not use siglock in try_oom_reaper()

Oleg has noted that siglock usage in try_oom_reaper is both pointless
and dangerous. signal_group_exit can be checked lockless. The problem
is that sighand becomes NULL in __exit_signal so we can crash.

Fixes: 3ef22dff ("oom, oom_reaper: try to reap tasks which skip regular OOM killer path")
Link: http://lkml.kernel.org/r/1464679423-30218-1-git-send-email-mhocko@kernel.org

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

parent 83b9355b

mm/oom_kill.c

+1 −6

Original line number	Diff line number	Diff line
		@@ -625,8 +625,6 @@ void try_oom_reaper(struct task_struct *tsk)
		if (atomic_read(&mm->mm_users) > 1) {
		rcu_read_lock();
		for_each_process(p) {
		bool exiting;

		if (!process_shares_mm(p, mm))
		continue;
		if (fatal_signal_pending(p))
		@@ -636,10 +634,7 @@ void try_oom_reaper(struct task_struct *tsk)
		* If the task is exiting make sure the whole thread group
		* is exiting and cannot acces mm anymore.
		*/
		spin_lock_irq(&p->sighand->siglock);
		exiting = signal_group_exit(p->signal);
		spin_unlock_irq(&p->sighand->siglock);
		if (exiting)
		if (signal_group_exit(p->signal))
		continue;

		/* Give up */