[PATCH] md: Fix 'rdev->nr_pending' count when retrying barrier requests

When retrying a failed BIO_RW_BARRIER request, we need to keep the reference
in ->nr_pending over the whole retry.  Currently, we only hold the reference
if the failed request is the *last* one to finish - which is silly, because it
would normally be the first to finish.

So move the rdev_dec_pending call up into the didn't-fail branch.  As the rdev
isn't used in the later code, calling rdev_dec_pending earlier doesn't hurt.
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/md/raid1.c

@@ -319,6 +319,7 @@ static int raid1_end_write_request(struct bio *bio, unsigned int bytes_done, int
 		set_bit(BarriersNotsupp, &conf->mirrors[mirror].rdev->flags);
 		set_bit(R1BIO_BarrierRetry, &r1_bio->state);
 		r1_bio->mddev->barriers_work = 0;
+		/* Don't rdev_dec_pending in this branch - keep it for the retry */
 	} else {
 		/*
 		 * this branch is our 'one mirror IO has finished' event handler:
@@ -365,6 +366,7 @@ static int raid1_end_write_request(struct bio *bio, unsigned int bytes_done, int
 				}
 			}
 		}
+		rdev_dec_pending(conf->mirrors[mirror].rdev, conf->mddev);
 	}
 	/*
 	 *
@@ -374,11 +376,9 @@ static int raid1_end_write_request(struct bio *bio, unsigned int bytes_done, int
 	if (atomic_dec_and_test(&r1_bio->remaining)) {
 		if (test_bit(R1BIO_BarrierRetry, &r1_bio->state)) {
 			reschedule_retry(r1_bio);
-			/* Don't dec_pending yet, we want to hold
-			 * the reference over the retry
-			 */
 			goto out;
 		}
+		/* it really is the end of this request */
 		if (test_bit(R1BIO_BehindIO, &r1_bio->state)) {
 			/* free extra copy of the data pages */
 			int i = bio->bi_vcnt;
@@ -393,8 +393,6 @@ static int raid1_end_write_request(struct bio *bio, unsigned int bytes_done, int
 		md_write_end(r1_bio->mddev);
 		raid_end_bio_io(r1_bio);
 	}
-
-	rdev_dec_pending(conf->mirrors[mirror].rdev, conf->mddev);
  out:
 	if (to_put)
 		bio_put(to_put);
@@ -1414,6 +1412,7 @@ static void raid1d(mddev_t *mddev)
 			 * Better resubmit without the barrier.
 			 * We know which devices to resubmit for, because
 			 * all others have had their bios[] entry cleared.
+			 * We already have a nr_pending reference on these rdevs.
 			 */
 			int i;
 			clear_bit(R1BIO_BarrierRetry, &r1_bio->state);