scsi,block: update SCSI to handle mixed merge failures

Update scsi_io_completion() such that it only fails requests till the
next error boundary and retry the leftover.  This enables block layer
to merge requests with different failfast settings and still behave
correctly on errors.  Allow merge of requests of different failfast
settings.

As SCSI is currently the only subsystem which follows failfast status,
there's no need to worry about other block drivers for now.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Niel Lambrechts <niel.lambrechts@gmail.com>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

block/blk-merge.c

@@ -380,12 +380,6 @@ static int attempt_merge(struct request_queue *q, struct request *req,
 	if (blk_integrity_rq(req) != blk_integrity_rq(next))
 		return 0;
 
-	/* don't merge requests of different failfast settings */
-	if (blk_failfast_dev(req)	!= blk_failfast_dev(next)	||
-	    blk_failfast_transport(req)	!= blk_failfast_transport(next)	||
-	    blk_failfast_driver(req)	!= blk_failfast_driver(next))
-		return 0;
-
 	/*
 	 * If we are allowed to merge, then append bio list
 	 * from next to rq and release next. merge_requests_fn

block/elevator.c

@@ -100,19 +100,6 @@ int elv_rq_merge_ok(struct request *rq, struct bio *bio)
 	if (bio_integrity(bio) != blk_integrity_rq(rq))
 		return 0;
 
-	/*
-	 * Don't merge if failfast settings don't match.
-	 *
-	 * FIXME: The negation in front of each condition is necessary
-	 * because bio and request flags use different bit positions
-	 * and the accessors return those bits directly.  This
-	 * ugliness will soon go away.
-	 */
-	if (!bio_failfast_dev(bio)	 != !blk_failfast_dev(rq)	||
-	    !bio_failfast_transport(bio) != !blk_failfast_transport(rq)	||
-	    !bio_failfast_driver(bio)	 != !blk_failfast_driver(rq))
-		return 0;
-
 	if (!elv_iosched_allow_merge(rq, bio))
 		return 0;
 

drivers/scsi/scsi_lib.c

@@ -897,8 +897,10 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
 			if (driver_byte(result) & DRIVER_SENSE)
 				scsi_print_sense("", cmd);
 		}
-		blk_end_request_all(req, -EIO);
-		scsi_next_command(cmd);
+		if (blk_end_request_err(req, -EIO))
+			scsi_requeue_command(q, cmd);
+		else
+			scsi_next_command(cmd);
 		break;
 	case ACTION_REPREP:
 		/* Unprep the request and put it back at the head of the queue.