mm: don't emit warning from pagefault_out_of_memory()

Commit c32b3cbe ("oom, PM: make OOM detection in the freezer path
raceless") inserted a WARN_ON() into pagefault_out_of_memory() in order
to warn when we raced with disabling the OOM killer.

Now, patch "oom, suspend: fix oom_killer_disable vs.  pm suspend
properly" introduced a timeout for oom_killer_disable().  Even if we
raced with disabling the OOM killer and the system is OOM livelocked,
the OOM killer will be enabled eventually (in 20 seconds by default) and
the OOM livelock will be solved.  Therefore, we no longer need to warn
when we raced with disabling the OOM killer.

Link: http://lkml.kernel.org/r/1473442120-7246-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jpSigned-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/oom_kill.c

@@ -1069,16 +1069,6 @@ void pagefault_out_of_memory(void)
 
 	if (!mutex_trylock(&oom_lock))
 		return;
-
-	if (!out_of_memory(&oc)) {
-		/*
-		 * There shouldn't be any user tasks runnable while the
-		 * OOM killer is disabled, so the current task has to
-		 * be a racing OOM victim for which oom_killer_disable()
-		 * is waiting for.
-		 */
-		WARN_ON(test_thread_flag(TIF_MEMDIE));
-	}
-
+	out_of_memory(&oc);
 	mutex_unlock(&oom_lock);
 }