The change to the oom_reaper to hold a mutex inside __oom_reap_task()
accidentally started calling mmput_async() on the local
mm before that variable got initialized, as reported by gcc
in linux-next:
mm/oom_kill.c: In function '__oom_reap_task':
mm/oom_kill.c:537:2: error: 'mm' may be used uninitialized in this function [-Werror=maybe-uninitialized]
This rearranges the code slightly back to the state before patch
but leaves the lock in place. The error handling in the function
still looks a bit confusing and could probably be improved
but I could not come up with a solution that made me happy
for now.
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
Fixes: mmotm ("oom_reaper: close race with exiting task")
---
mm/oom_kill.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 1685890d424e..255cb5f48019 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -447,7 +447,7 @@ static bool __oom_reap_task(struct task_struct *tsk)
struct task_struct *p;
struct zap_details details = {.check_swap_entries = true,
.ignore_dirty = true};
- bool ret = true;
+ bool ret;
/*
* We have to make sure to not race with the victim exit path
@@ -472,13 +472,16 @@ static bool __oom_reap_task(struct task_struct *tsk)
* is no mm.
*/
p = find_lock_task_mm(tsk);
- if (!p)
- goto unlock_oom;
+ if (!p) {
+ mutex_unlock(&oom_lock);
+ return true;
+ }
mm = p->mm;
if (!atomic_inc_not_zero(&mm->mm_users)) {
task_unlock(p);
- goto unlock_oom;
+ mutex_unlock(&oom_lock);
+ return true;
}
task_unlock(p);
@@ -527,6 +530,7 @@ static bool __oom_reap_task(struct task_struct *tsk)
* to release its memory.
*/
set_bit(MMF_OOM_REAPED, &mm->flags);
+ ret = true;
unlock_oom:
mutex_unlock(&oom_lock);
/*
--
2.7.0
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