[PATCH] make AS work nicely with SCSI

This allows SCSI to survive the I/O queueing stress harness with AS.

Jens has signed off on it, and Mark Havercamp confirms it also
eliminates the test induced hangs for him too.

drivers/block/ll_rw_blk.c

@@ -1522,6 +1522,7 @@ void blk_requeue_request(request_queue_t *q, struct request *rq)
  * @rq:		request to be inserted
  * @at_head:	insert request at head or tail of queue
  * @data:	private data
+ * @reinsert:	true if request it a reinsertion of previously processed one
  *
  * Description:
  *    Many block devices need to execute commands asynchronously, so they don't
@@ -1536,7 +1537,7 @@ void blk_requeue_request(request_queue_t *q, struct request *rq)
  *    host that is unable to accept a particular command.
  */
 void blk_insert_request(request_queue_t *q, struct request *rq,
-			int at_head, void *data)
+			int at_head, void *data, int reinsert)
 {
 	unsigned long flags;
 
@@ -1554,11 +1555,15 @@ void blk_insert_request(request_queue_t *q, struct request *rq,
 	/*
 	 * If command is tagged, release the tag
 	 */
-	if (blk_rq_tagged(rq))
-		blk_queue_end_tag(q, rq);
+	if(reinsert) {
+		blk_requeue_request(q, rq);
+	} else {
+		if (blk_rq_tagged(rq))
+			blk_queue_end_tag(q, rq);
 
-	drive_stat_acct(rq, rq->nr_sectors, 1);
-	__elv_add_request(q, rq, !at_head, 0);
+		drive_stat_acct(rq, rq->nr_sectors, 1);
+		__elv_add_request(q, rq, !at_head, 0);
+	}
 	q->request_fn(q);
 	spin_unlock_irqrestore(q->queue_lock, flags);
 }

drivers/scsi/scsi_lib.c

@@ -69,7 +69,7 @@ int scsi_insert_special_req(struct scsi_request *sreq, int at_head)
 	 */
 	sreq->sr_request->flags &= ~REQ_DONTPREP;
 	blk_insert_request(sreq->sr_device->request_queue, sreq->sr_request,
-		       	   at_head, sreq);
+		       	   at_head, sreq, 0);
 	return 0;
 }
 
@@ -147,7 +147,7 @@ int scsi_queue_insert(struct scsi_cmnd *cmd, int reason)
 	 * function.  The SCSI request function detects the blocked condition
 	 * and plugs the queue appropriately.
 	 */
-	blk_insert_request(device->request_queue, cmd->request, 1, cmd);
+	blk_insert_request(device->request_queue, cmd->request, 1, cmd, 1);
 	return 0;
 }
 
@@ -445,7 +445,7 @@ static void scsi_run_queue(struct request_queue *q)
 static void scsi_requeue_command(struct request_queue *q, struct scsi_cmnd *cmd)
 {
 	cmd->request->flags &= ~REQ_DONTPREP;
-	blk_insert_request(q, cmd->request, 1, cmd);
+	blk_insert_request(q, cmd->request, 1, cmd, 1);
 
 	scsi_run_queue(q);
 }

include/linux/blkdev.h

@@ -491,7 +491,7 @@ extern void blk_attempt_remerge(request_queue_t *, struct request *);
 extern void __blk_attempt_remerge(request_queue_t *, struct request *);
 extern struct request *blk_get_request(request_queue_t *, int, int);
 extern void blk_put_request(struct request *);
-extern void blk_insert_request(request_queue_t *, struct request *, int, void *);
+extern void blk_insert_request(request_queue_t *, struct request *, int, void *, int);
 extern void blk_requeue_request(request_queue_t *, struct request *);
 extern void blk_plug_device(request_queue_t *);
 extern int blk_remove_plug(request_queue_t *);