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: 3ef22dfff239 ("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>

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index dfb1ab61fb2374379ca014ee4f764366dc20c081..acbc432d1a52778d746879d652fd4c2001075868 100644 (file)
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -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 */