md/raid5: Refactor raid5_make_request loop

Break immediately if raid5_get_active_stripe() returns NULL and deindent
the rest of the loop. Annotate this check with an unlikely().

This makes the code easier to read and reduces the indentation level.

No functional changes intended.
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Guoqing Jiang <guoqing.jiang@linux.dev>
Signed-off-by: Song Liu <song@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/md/raid5.c

@@ -5902,7 +5902,12 @@ static bool raid5_make_request(struct mddev *mddev, struct bio * bi)
 
 		sh = raid5_get_active_stripe(conf, new_sector, previous,
 				       (bi->bi_opf & REQ_RAHEAD), 0);
-		if (sh) {
+		if (unlikely(!sh)) {
+			/* cannot get stripe, just give-up */
+			bi->bi_status = BLK_STS_IOERR;
+			break;
+		}
+
 		if (unlikely(previous)) {
 			/* expansion might have moved on while waiting for a
 			 * stripe, so we must do the range check again.
@@ -5926,19 +5931,18 @@ static bool raid5_make_request(struct mddev *mddev, struct bio * bi)
 				goto retry;
 			}
 		}
+
 		if (read_seqcount_retry(&conf->gen_lock, seq)) {
-				/* Might have got the wrong stripe_head
-				 * by accident
-				 */
+			/* Might have got the wrong stripe_head by accident */
 			raid5_release_stripe(sh);
 			goto retry;
 		}
 
 		if (test_bit(STRIPE_EXPANDING, &sh->state) ||
 		    !add_stripe_bio(sh, bi, dd_idx, rw, previous)) {
-				/* Stripe is busy expanding or
-				 * add failed due to overlap.  Flush everything
-				 * and wait a while
+			/*
+			 * Stripe is busy expanding or add failed due to
+			 * overlap. Flush everything and wait a while.
 			 */
 			md_wakeup_thread(mddev->thread);
 			raid5_release_stripe(sh);
@@ -5946,6 +5950,7 @@ static bool raid5_make_request(struct mddev *mddev, struct bio * bi)
 			do_prepare = true;
 			goto retry;
 		}
+
 		if (do_flush) {
 			set_bit(STRIPE_R5C_PREFLUSH, &sh->state);
 			/* we only need flush for one stripe */
@@ -5958,12 +5963,8 @@ static bool raid5_make_request(struct mddev *mddev, struct bio * bi)
 		    (bi->bi_opf & REQ_SYNC) &&
 		    !test_and_set_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
 			atomic_inc(&conf->preread_active_stripes);
+
 		release_stripe_plug(mddev, sh);
-		} else {
-			/* cannot get stripe for read-ahead, just give-up */
-			bi->bi_status = BLK_STS_IOERR;
-			break;
-		}
 	}
 	finish_wait(&conf->wait_for_overlap, &w);