From: Michal Hocko <mhocko@xxxxxxxx>
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")
Suggested-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
---
Hi Andrew,
Oleg has noticed this while reviewing http://lkml.kernel.org/r/20160530173505.GA25287@xxxxxxxxxx
this should go in 4.7.
mm/oom_kill.c | 7 +------
1 file changed, 1 insertion(+), 6 deletions(-)
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index e01cc3e2e755..25eac62c190c 100644
--- 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 */
--
2.8.1
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