[PATCH v2 4/4] md/raid1: simplify raid1_write_request() error handling

[Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>]

raid1_write_request() increments rdev->nr_pending before checking the
badblocks and then immediately decrements it again when a device is
skipped. Move the increment until after the checks succeed so the
reference accounting is easier to follow.

Consolidate the failure paths so that each error label releases exactly
the resources acquired up to that point. err_dec_pending drops pending
references and frees the r1bio, while err_allow_barrier handles the
barrier release before returning.

When a REQ_ATOMIC write cannot be satisfied due to a badblock range,
complete the bio with BLK_STS_NOTSUPP rather than reporting an I/O
error, since the operation is unsupported rather than having failed
during I/O.

Rename max_write_sectors to max_sectors and remove the redundant local
copy.

Signed-off-by: Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>
---
Changes in v2:
 - new patch, depends on patch 1.
---
 drivers/md/raid1.c | 59 +++++++++++++++++++++++-----------------------
 1 file changed, 30 insertions(+), 29 deletions(-)

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index f0e1c7125972..dc0b7b8bc2f8 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -1502,29 +1502,29 @@ static void raid1_start_write_behind(struct mddev *mddev, struct r1bio *r1_bio,
 }
 
 static bool raid1_write_request(struct mddev *mddev, struct bio *bio,
-				int max_write_sectors)
+				int max_sectors)
 {
 	struct r1conf *conf = mddev->private;
 	struct r1bio *r1_bio;
 	int i, disks, k;
 	unsigned long flags;
 	int first_clone;
-	int max_sectors;
 	bool write_behind = false;
-	bool is_discard = (bio_op(bio) == REQ_OP_DISCARD);
+	bool nowait = bio->bi_opf & REQ_NOWAIT;
+	bool is_discard = op_is_discard(bio->bi_opf);
 	sector_t sector = bio->bi_iter.bi_sector;
 
 	if (mddev_is_clustered(mddev) &&
-	    mddev->cluster_ops->area_resyncing(mddev, WRITE,
-		     bio->bi_iter.bi_sector, bio_end_sector(bio))) {
+	    mddev->cluster_ops->area_resyncing(mddev, WRITE, sector,
+					       bio_end_sector(bio))) {
 
-		if (bio->bi_opf & REQ_NOWAIT) {
+		if (nowait) {
 			bio_wouldblock_error(bio);
 			return false;
 		}
 		wait_event_idle(conf->wait_barrier,
 				!mddev->cluster_ops->area_resyncing(mddev, WRITE,
-								    bio->bi_iter.bi_sector,
+								    sector,
 								    bio_end_sector(bio)));
 	}
 
@@ -1533,20 +1533,18 @@ static bool raid1_write_request(struct mddev *mddev, struct bio *bio,
 	 * thread has put up a bar for new requests.
 	 * Continue immediately if no resync is active currently.
 	 */
-	if (!wait_barrier(conf, bio->bi_iter.bi_sector,
-				bio->bi_opf & REQ_NOWAIT)) {
+	if (!wait_barrier(conf, sector, nowait)) {
 		bio_wouldblock_error(bio);
 		return false;
 	}
 
 	if (!wait_blocked_rdev(mddev, bio)) {
 		bio_wouldblock_error(bio);
-		allow_barrier(conf, sector);
-		return false;
+		goto err_allow_barrier;
 	}
 
 	r1_bio = alloc_r1bio(mddev, bio);
-	r1_bio->sectors = max_write_sectors;
+	r1_bio->sectors = max_sectors;
 
 	/* first select target devices under rcu_lock and
 	 * inc refcount on their rdev.  Record them by setting
@@ -1560,7 +1558,6 @@ static bool raid1_write_request(struct mddev *mddev, struct bio *bio,
 	 */
 
 	disks = conf->raid_disks * 2;
-	max_sectors = r1_bio->sectors;
 	for (i = 0;  i < disks; i++) {
 		struct md_rdev *rdev = conf->mirrors[i].rdev;
 
@@ -1576,23 +1573,21 @@ static bool raid1_write_request(struct mddev *mddev, struct bio *bio,
 		if (!rdev || test_bit(Faulty, &rdev->flags))
 			continue;
 
-		atomic_inc(&rdev->nr_pending);
 		if (test_bit(WriteErrorSeen, &rdev->flags)) {
 			sector_t first_bad;
 			sector_t bad_sectors;
 			int is_bad;
 
-			is_bad = is_badblock(rdev, r1_bio->sector, max_sectors,
+			is_bad = is_badblock(rdev, sector, max_sectors,
 					     &first_bad, &bad_sectors);
-			if (is_bad && first_bad <= r1_bio->sector) {
+			if (is_bad && first_bad <= sector) {
 				/* Cannot write here at all */
-				bad_sectors -= (r1_bio->sector - first_bad);
+				bad_sectors -= (sector - first_bad);
 				if (bad_sectors < max_sectors)
 					/* mustn't write more than bad_sectors
 					 * to other devices yet
 					 */
 					max_sectors = bad_sectors;
-				rdev_dec_pending(rdev, mddev);
 				continue;
 			}
 			if (is_bad) {
@@ -1606,15 +1601,18 @@ static bool raid1_write_request(struct mddev *mddev, struct bio *bio,
 				 * the benefit.
 				 */
 				if (bio->bi_opf & REQ_ATOMIC) {
-					rdev_dec_pending(rdev, mddev);
-					goto err_handle;
+					bio->bi_status = BLK_STS_NOTSUPP;
+					bio_endio(bio);
+					goto err_dec_pending;
 				}
 
-				good_sectors = first_bad - r1_bio->sector;
+				good_sectors = first_bad - sector;
 				if (good_sectors < max_sectors)
 					max_sectors = good_sectors;
 			}
 		}
+
+		atomic_inc(&rdev->nr_pending);
 		r1_bio->bios[i] = bio;
 	}
 
@@ -1630,10 +1628,8 @@ static bool raid1_write_request(struct mddev *mddev, struct bio *bio,
 	if (max_sectors < bio_sectors(bio)) {
 		bio = bio_submit_split_bioset(bio, max_sectors,
 					      &conf->bio_split);
-		if (!bio) {
-			set_bit(R1BIO_Returned, &r1_bio->state);
-			goto err_handle;
-		}
+		if (!bio)
+			goto err_dec_pending;
 
 		r1_bio->master_bio = bio;
 		r1_bio->sectors = max_sectors;
@@ -1677,7 +1673,7 @@ static bool raid1_write_request(struct mddev *mddev, struct bio *bio,
 		mbio->bi_opf &= ~REQ_NOWAIT;
 		r1_bio->bios[i] = mbio;
 
-		mbio->bi_iter.bi_sector	= (r1_bio->sector + rdev->data_offset);
+		mbio->bi_iter.bi_sector	= sector + rdev->data_offset;
 		mbio->bi_end_io	= raid1_end_write_request;
 		if (test_bit(FailFast, &rdev->flags) &&
 		    !test_bit(WriteMostly, &rdev->flags) &&
@@ -1686,7 +1682,7 @@ static bool raid1_write_request(struct mddev *mddev, struct bio *bio,
 		mbio->bi_private = r1_bio;
 
 		atomic_inc(&r1_bio->remaining);
-		mddev_trace_remap(mddev, mbio, r1_bio->sector);
+		mddev_trace_remap(mddev, mbio, sector);
 		/* flush_pending_writes() needs access to the rdev so...*/
 		mbio->bi_bdev = (void *)rdev;
 		if (!raid1_add_bio_to_plug(mddev, mbio, raid1_unplug, disks)) {
@@ -1701,9 +1697,10 @@ static bool raid1_write_request(struct mddev *mddev, struct bio *bio,
 
 	/* In case raid1d snuck in to freeze_array */
 	wake_up_barrier(conf);
+
 	return true;
 
-err_handle:
+err_dec_pending:
 	for (k = 0; k < i; k++) {
 		if (r1_bio->bios[k]) {
 			rdev_dec_pending(conf->mirrors[k].rdev, mddev);
@@ -1711,7 +1708,11 @@ static bool raid1_write_request(struct mddev *mddev, struct bio *bio,
 		}
 	}
 
-	raid_end_bio_io(r1_bio);
+	free_r1bio(r1_bio);
+
+err_allow_barrier:
+	allow_barrier(conf, sector);
+
 	return false;
 }
 
-- 
2.43.0