[PATCH] CFQ: bad locking in changed_ioprio()

When the ioprio code recently got juggled a bit, a bug was introduced.
changed_ioprio() is no longer called with interrupts disabled, so using
plain spin_lock() on the queue_lock is a bug.
Signed-off-by: NJens Axboe <jens.axboe@oracle.com>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

block/cfq-iosched.c

@@ -1215,11 +1215,12 @@ static inline void changed_ioprio(struct cfq_io_context *cic)
 {
 	struct cfq_data *cfqd = cic->key;
 	struct cfq_queue *cfqq;
+	unsigned long flags;
 
 	if (unlikely(!cfqd))
 		return;
 
-	spin_lock(cfqd->queue->queue_lock);
+	spin_lock_irqsave(cfqd->queue->queue_lock, flags);
 
 	cfqq = cic->cfqq[ASYNC];
 	if (cfqq) {
@@ -1236,7 +1237,7 @@ static inline void changed_ioprio(struct cfq_io_context *cic)
 	if (cfqq)
 		cfq_mark_cfqq_prio_changed(cfqq);
 
-	spin_unlock(cfqd->queue->queue_lock);
+	spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
 }
 
 static void cfq_ioc_set_ioprio(struct io_context *ioc)