[PATCH] fix wait_task_inactive race

When a task is put to sleep, it is dequeued from the runqueue while it is
still running.  The problem is that one some arches that have non-atomic
scheduling, the runqueue lock can be dropped and retaken in schedule() before
the task actually schedules off, and wait_task_inactive did not account for
this.
Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

kernel/sched.c

@@ -867,7 +867,7 @@ void wait_task_inactive(task_t * p)
 repeat:
 	rq = task_rq_lock(p, &flags);
 	/* Must be off runqueue entirely, not preempted. */
-	if (unlikely(p->array)) {
+	if (unlikely(p->array || task_running(rq, p))) {
 		/* If it's preempted, we yield.  It could be a while. */
 		preempted = !task_running(rq, p);
 		task_rq_unlock(rq, &flags);