oom: PF_EXITING check should take mm into account
Oleg Nesterov [Tue, 10 Aug 2010 00:18:44 +0000 (17:18 -0700)]
select_bad_process() checks PF_EXITING to detect the task which is going
to release its memory, but the logic is very wrong.

- a single process P with the dead group leader disables
  select_bad_process() completely, it will always return
  ERR_PTR() while P can live forever

- if the PF_EXITING task has already released its ->mm
  it doesn't make sense to expect it is goiing to free
  more memory (except task_struct/etc)

Change the code to ignore the PF_EXITING tasks without ->mm.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: David Rientjes <rientjes@google.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/oom_kill.c

index 7c0dc41..0a6e466 100644 (file)
@@ -287,7 +287,7 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
                 * the process of exiting and releasing its resources.
                 * Otherwise we could get an easy OOM deadlock.
                 */
-               if (p->flags & PF_EXITING) {
+               if ((p->flags & PF_EXITING) && p->mm) {
                        if (p != current)
                                return ERR_PTR(-1UL);