[PATCH 10/13] block: Improve blk_zone_write_plug_bio_merged()

[Damien Le Moal <dlemoal@kernel.org>]

Improve blk_zone_write_plug_bio_merged() to check that we succefully get
a reference on the zone write plugi of the merged BIO, as expected since
for a merge we already have at least one request and one BIO referencing
the zone write plug. Comments in this function are also improved to
better explain the references to the BIO zone write plug.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
---
 block/blk-zoned.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/block/blk-zoned.c b/block/blk-zoned.c
index b551fe4e684f..d962ba7c9ae1 100644
--- a/block/blk-zoned.c
+++ b/block/blk-zoned.c
@@ -866,11 +866,16 @@ void blk_zone_write_plug_bio_merged(struct bio *bio)
 	bio_set_flag(bio, BIO_ZONE_WRITE_PLUGGING);
 
 	/*
-	 * Increase the plug reference count and advance the zone write
-	 * pointer offset.
+	 * Get a reference on the zone write plug of the target zone and advance
+	 * the zone write pointer offset. Given that this is a merge, we already
+	 * have at least one request and one BIO referencing the zone write
+	 * plug. So this should not fail.
 	 */
 	zwplug = disk_get_zone_wplug(bio->bi_bdev->bd_disk,
 				     bio->bi_iter.bi_sector);
+	if (WARN_ON_ONCE(!zwplug))
+		return;
+
 	spin_lock_irqsave(&zwplug->lock, flags);
 	zwplug->wp_offset += bio_sectors(bio);
 	spin_unlock_irqrestore(&zwplug->lock, flags);
-- 
2.44.0