[PATCH v4 25/25] md/raid5: split reshape bios before bitmap accounting

From: Yu Kuai <yukuai@fygo.io>

RAID5 maps array sectors through different geometries before and after the
reshape position. During llbitmap reshape, md core cannot account one bio
against both geometries as a single bitmap range, because the old and new
bitmap mappings can cover different chunks.

Split bios that cross reshape_position before md_account_bio(), so the
bitmap only sees ranges that belong to one side of the reshape boundary.

mddev_bio_split_at_reshape_offset() uses bio_submit_split_bioset(), which
submits the remainder immediately and returns the front split bio. If that
front bio later has to wait for reshape, md_handle_request() must not retry
the original bio pointer, because after the split that pointer is the
already-submitted remainder. Track whether the split happened, clear the
temporary BLK_STS_RESOURCE status after the internal clone completion, and
resubmit the front bio directly after the reshape wait. Keep the old
return-false retry path for unsplit bios, where md_handle_request() still
owns the same bio.

Signed-off-by: Yu Kuai <yukuai@fygo.io>
---
 drivers/md/raid5.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 896aa522f446..9b47d9a277f9 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c

@@ -6148,9 +6148,11 @@ static bool raid5_make_request(struct mddev *mddev, struct bio * bi)
 	struct r5conf *conf = mddev->private;
 	const int rw = bio_data_dir(bi);
 	struct stripe_request_ctx *ctx;
+	struct bio *front_bio;
 	sector_t logical_sector;
 	enum stripe_result res;
 	int s, stripe_cnt;
+	bool split = false;
 	bool on_wq;
 
 	if (unlikely(bi->bi_opf & REQ_PREFLUSH)) {

@@ -6184,6 +6186,18 @@ static bool raid5_make_request(struct mddev *mddev, struct bio * bi)
 		return true;
 	}
 
+	front_bio = bi;
+	bi = mddev_bio_split_at_reshape_offset(mddev, bi, NULL,
+					       &conf->bio_split);
+	if (!bi) {
+		if (rw == WRITE)
+			md_write_end(mddev);
+		return true;
+	}
+	if (bi != front_bio)
+		split = true;
+	front_bio = bi;
+
 	logical_sector = bi->bi_iter.bi_sector & ~((sector_t)RAID5_STRIPE_SECTORS(conf)-1);
 	bi->bi_next = NULL;
 

@@ -6284,6 +6298,11 @@ static bool raid5_make_request(struct mddev *mddev, struct bio * bi)
 		bio_endio(bi);
 
 		wait_for_completion(&done);
+		front_bio->bi_status = BLK_STS_OK;
+		if (split) {
+			submit_bio_noacct(front_bio);
+			return true;
+		}
 		return false;
 	}
 

-- 
2.51.0