[PATCH 3/7] md/raid10: handle atomic writes that require splitting

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

If a request already requires splitting when entering
raid10_write_request(), the current code allows it to proceed until it
eventually reaches the split path. Along the way, the bio may instead
fail due to other conditions and return a different status, even though
the request was invalid as an atomic write from the beginning.

Additionally, an otherwise valid atomic write may later require
splitting because bad blocks reduce the writable range. In this case,
the bio currently completes with either EINVAL or EIO, whereas it should
complete with EIO consistently.

Fixes: a1d9b4fd42d9 ("md/raid10: Atomic write support")
Signed-off-by: Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>
---
 drivers/md/raid10.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index bd322eccdc3f..840f0446c231 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1356,6 +1356,13 @@ static bool raid10_write_request(struct mddev *mddev, struct bio *bio,
 	int i, k;
 	sector_t sectors;
 	int max_sectors;
+	bool atomic = bio->bi_opf & REQ_ATOMIC;
+
+	if (atomic && r10_bio->sectors != bio_sectors(bio)) {
+		bio_endio_status(bio, BLK_STS_INVAL);
+		free_r10bio(r10_bio);
+		return false;
+	}
 
 	if ((mddev_is_clustered(mddev) &&
 	     mddev->cluster_ops->area_resyncing(mddev, WRITE,
@@ -1464,16 +1471,6 @@ static bool raid10_write_request(struct mddev *mddev, struct bio *bio,
 			if (is_bad) {
 				int good_sectors;
 
-				/*
-				 * We cannot atomically write this, so just
-				 * error in that case. It could be possible to
-				 * atomically write other mirrors, but the
-				 * complexity of supporting that is not worth
-				 * the benefit.
-				 */
-				if (bio->bi_opf & REQ_ATOMIC)
-					goto err_handle;
-
 				good_sectors = first_bad - dev_sector;
 				if (good_sectors < max_sectors)
 					max_sectors = good_sectors;
@@ -1493,6 +1490,9 @@ static bool raid10_write_request(struct mddev *mddev, struct bio *bio,
 		r10_bio->sectors = max_sectors;
 
 	if (r10_bio->sectors < bio_sectors(bio)) {
+		if (atomic)
+			goto err_handle;
+
 		allow_barrier(conf);
 		bio = bio_submit_split_bioset(bio, r10_bio->sectors,
 					      &conf->bio_split);
-- 
2.43.0