libata: fix locking around blk_abort_request()

blk_abort_request() expectes queue lock to be held by the caller.
Grab it before calling the function.

Lack of this synchronization led to infinite loop on corrupt
q->timeout_list.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: stable@kernel.org
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/libata-eh.c

@@ -879,6 +879,8 @@ static void ata_eh_set_pending(struct ata_port *ap, int fastdrain)
 void ata_qc_schedule_eh(struct ata_queued_cmd *qc)
 {
 	struct ata_port *ap = qc->ap;
+	struct request_queue *q = qc->scsicmd->device->request_queue;
+	unsigned long flags;
 
 	WARN_ON(!ap->ops->error_handler);
 
@@ -890,7 +892,9 @@ void ata_qc_schedule_eh(struct ata_queued_cmd *qc)
 	 * Note that ATA_QCFLAG_FAILED is unconditionally set after
 	 * this function completes.
 	 */
+	spin_lock_irqsave(q->queue_lock, flags);
 	blk_abort_request(qc->scsicmd->request);
+	spin_unlock_irqrestore(q->queue_lock, flags);
 }
 
 /**