[PATCH] fix OOM killing of swapoff

These days, if you swapoff when there isn't enough memory, OOM killer gives
"BUG: scheduling while atomic" and the machine hangs: badness() needs to do
its PF_SWAPOFF return after the task_unlock (tasklist_lock is also held
here, so p isn't going to be freed: PF_SWAPOFF might get turned off at any
moment, but that doesn't really matter).
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

mm/oom_kill.c

@@ -60,12 +60,6 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
 		return 0;
 	}
 
-	/*
-	 * swapoff can easily use up all memory, so kill those first.
-	 */
-	if (p->flags & PF_SWAPOFF)
-		return ULONG_MAX;
-
 	/*
 	 * The memory size of the process is the basis for the badness.
 	 */
@@ -76,6 +70,12 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
 	 */
 	task_unlock(p);
 
+	/*
+	 * swapoff can easily use up all memory, so kill those first.
+	 */
+	if (p->flags & PF_SWAPOFF)
+		return ULONG_MAX;
+
 	/*
 	 * Processes which fork a lot of child processes are likely
 	 * a good choice. We add half the vmsize of the children if they