oom: fix tasklist_lock leak

Commit 0aad4b3124 ("oom: fold __out_of_memory into out_of_memory")
introduced a tasklist_lock leak.  Then it caused following obvious
danger warnings and panic.

    ================================================
    [ BUG: lock held when returning to user space! ]
    ------------------------------------------------
    rsyslogd/1422 is leaving the kernel with locks still held!
    1 lock held by rsyslogd/1422:
     #0:  (tasklist_lock){.+.+.+}, at: [<ffffffff810faf64>] out_of_memory+0x164/0x3f0
    BUG: scheduling while atomic: rsyslogd/1422/0x00000002
    INFO: lockdep is turned off.

This patch fixes it.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 3 deletions

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 17d48a67e7b..c48c5ef3ccf 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -646,6 +646,7 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
         unsigned long freed = 0;
         unsigned int points;
         enum oom_constraint constraint = CONSTRAINT_NONE;
+        int killed = 0;
 
         blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
         if (freed > 0)
@@ -683,7 +684,7 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
                 if (!oom_kill_process(current, gfp_mask, order, 0, totalpages,
                                 NULL, nodemask,
                                 "Out of memory (oom_kill_allocating_task)"))
-                        return;
+                        goto out;
         }
 
 retry:
@@ -691,7 +692,7 @@ retry:
                         constraint == CONSTRAINT_MEMORY_POLICY ? nodemask :
                                                                  NULL);
         if (PTR_ERR(p) == -1UL)
-                return;
+                goto out;
 
         /* Found nothing?!?! Either we hang forever, or we panic. */
         if (!p) {
@@ -703,13 +704,15 @@ retry:
         if (oom_kill_process(p, gfp_mask, order, points, totalpages, NULL,
                                 nodemask, "Out of memory"))
                 goto retry;
+        killed = 1;
+out:
         read_unlock(&tasklist_lock);
 
         /*
          * Give "p" a good chance of killing itself before we
          * retry to allocate memory unless "p" is current
          */
-        if (!test_thread_flag(TIF_MEMDIE))
+        if (killed && !test_thread_flag(TIF_MEMDIE))
                 schedule_timeout_uninterruptible(1);
 }