[PATCH v3 4/7] md/raid10: remove unnecessary barrier around bio_submit_split_bioset()

raid10_write_request() drops the barrier before calling
bio_submit_split_bioset() and reacquires it afterwards. This is no
longer necessary because the split bio cannot re-enter
raid10_write_request() while the barrier is held.

The allow_barrier()/wait_barrier() pair was introduced by commit
e820d55cb99d ("md: fix raid10 hang issue caused by barrier") when
submit_flushes() called md_handle_request() directly, allowing re-entry
into raid10_write_request(). Since v5.2, submit_flushes() has instead
gone through submit_bio(), eliminating that recursion. submit_flushes()
was later removed entirely by commit b75197e86e6d ("md: Remove flush
handling").

Currently, raid10_write_request() is only entered from the bio
submission path, so the split bio submitted by bio_submit_split_bioset()
cannot recurse back into wait_barrier().

Remove the redundant allow_barrier()/wait_barrier() pair around
bio_submit_split_bioset().

Signed-off-by: Abd-Alrhman Masalkhi <[email protected]>
---
Changes in v3:
 - No changes.
 - Link to v2: https://lore.kernel.org/linux-raid/[email protected]/

Changes in v2:
 - Expand the commit message to explain why the
   allow_barrier()/wait_barrier() pair is no longer needed.
 - Link to v1: https://lore.kernel.org/linux-raid/[email protected]/
---
 drivers/md/raid10.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 3480fc7907f0..2574f60dd771 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1487,10 +1487,8 @@ static bool raid10_write_request(struct mddev *mddev, struct bio *bio,
 		if (atomic)
 			goto err_handle;
 
-		allow_barrier(conf);
 		bio = bio_submit_split_bioset(bio, r10_bio->sectors,
 					      &conf->bio_split);
-		wait_barrier(conf, false);
 		if (!bio) {
 			set_bit(R10BIO_Returned, &r10_bio->state);
 			goto err_handle;
-- 
2.43.0