[SCSI] limit state transitions in scsi_internal_device_unblock

scsi timeout on two or more devices may cause extremely long execution
time for user applications because SDEV_OFFLINE state is changed to
SDEV_RUNNING state during scsi error recovery procedures triggered by
a bus reset or a host reset of scsi LLD, and scsi timeout can happens
on the same devices many times.

This happens because scsi_internal_device_unblock() changes device's
state to SDEV_RUNNING even if a device in other states than SDEV_BLOCK,
while the following two transitions are required in this function.

  SDEV_BLOCK -> SDEV_RUNNING
  SDEV_CREATED_BLOCK -> SDEV_CREATED

Otherwise, it returns -EINVAL.

Signed-off-by: Takahiro Yasui <tyasui@redhat.com>
[matthew@wil.cx: supplied rewritten base for patch]
Signed-off-by: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

drivers/scsi/scsi_lib.c

@@ -2441,20 +2441,18 @@ int
 scsi_internal_device_unblock(struct scsi_device *sdev)
 {
 	struct request_queue *q = sdev->request_queue; 
-	int err;
 	unsigned long flags;
 
 	/* 
 	 * Try to transition the scsi device to SDEV_RUNNING
 	 * and goose the device queue if successful.  
 	 */
-	err = scsi_device_set_state(sdev, SDEV_RUNNING);
-	if (err) {
-		err = scsi_device_set_state(sdev, SDEV_CREATED);
-
-		if (err)
-			return err;
-	}
+	if (sdev->sdev_state == SDEV_BLOCK)
+		sdev->sdev_state = SDEV_RUNNING;
+	else if (sdev->sdev_state == SDEV_CREATED_BLOCK)
+		sdev->sdev_state = SDEV_CREATED;
+	else
+		return -EINVAL;
 
 	spin_lock_irqsave(q->queue_lock, flags);
 	blk_start_queue(q);