[SCSI] Make scsi_free_queue() kill pending SCSI commands

Make sure that SCSI device removal via scsi_remove_host() does finish
all pending SCSI commands. Currently that's not the case and hence
removal of a SCSI host during I/O can cause a deadlock. See also
"blkdev_issue_discard() hangs forever if underlying storage device is
removed" (http://bugzilla.kernel.org/show_bug.cgi?id=40472). See also
http://lkml.org/lkml/2011/8/27/6.
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Cc: <stable@kernel.org>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

drivers/scsi/hosts.c

@@ -286,6 +286,7 @@ static void scsi_host_dev_release(struct device *dev)
 {
 	struct Scsi_Host *shost = dev_to_shost(dev);
 	struct device *parent = dev->parent;
+	struct request_queue *q;
 
 	scsi_proc_hostdir_rm(shost->hostt);
 
@@ -293,9 +294,11 @@ static void scsi_host_dev_release(struct device *dev)
 		kthread_stop(shost->ehandler);
 	if (shost->work_q)
 		destroy_workqueue(shost->work_q);
-	if (shost->uspace_req_q) {
-		kfree(shost->uspace_req_q->queuedata);
-		scsi_free_queue(shost->uspace_req_q);
+	q = shost->uspace_req_q;
+	if (q) {
+		kfree(q->queuedata);
+		q->queuedata = NULL;
+		scsi_free_queue(q);
 	}
 
 	scsi_destroy_command_freelist(shost);

drivers/scsi/scsi_lib.c

@@ -1698,6 +1698,15 @@ struct request_queue *scsi_alloc_queue(struct scsi_device *sdev)
 
 void scsi_free_queue(struct request_queue *q)
 {
+	unsigned long flags;
+
+	WARN_ON(q->queuedata);
+
+	/* cause scsi_request_fn() to kill all non-finished requests */
+	spin_lock_irqsave(q->queue_lock, flags);
+	q->request_fn(q);
+	spin_unlock_irqrestore(q->queue_lock, flags);
+
 	blk_cleanup_queue(q);
 }