[PATCH v2 3/7] md/raid10: consistently fail atomic writes that require splitting

[Abd-Alrhman Masalkhi]

RAID10 currently handles one badblock path explicitly by failing atomic
writes with EIO. However, another badblock path can also reduce the
writable range and force the bio through bio_submit_split_bioset(),
which implicitly completes the bio with EINVAL.

Fix this by handling atomic writes in the common split check. If RAID10
determines that an atomic write would require splitting, complete the
bio with EIO.

Fixes: a1d9b4fd42d9 ("md/raid10: Atomic write support")
Signed-off-by: Abd-Alrhman Masalkhi <abd.masalkhi@xxxxxxxxx>
---
Changes in v2:
 - Drop the early atomic write split check from raid10_write_request()
   and rely on queue limits instead.
 - Link to v1: https://lore.kernel.org/linux-raid/20260623072456.333437-4-abd.masalkhi@xxxxxxxxx/
---
 drivers/md/raid10.c | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index bd322eccdc3f..3480fc7907f0 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1356,6 +1356,7 @@ 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 ((mddev_is_clustered(mddev) &&
 	     mddev->cluster_ops->area_resyncing(mddev, WRITE,
@@ -1464,16 +1465,6 @@ 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 +1484,9 @@ 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