From: Michal Hocko <mhocko@xxxxxxxx>
Subject: 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@xxxxxxxxxx
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Suggested-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/oom_kill.c | 7 +------
1 file changed, 1 insertion(+), 6 deletions(-)
diff -puN mm/oom_kill.c~mm-oom_reaper-do-not-use-siglock-in-try_oom_reaper mm/oom_kill.c
--- a/mm/oom_kill.c~mm-oom_reaper-do-not-use-siglock-in-try_oom_reaper
+++ a/mm/oom_kill.c
@@ -625,8 +625,6 @@ void try_oom_reaper(struct task_struct *
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 *
* 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 */
_
--
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