block: Improve blk_zone_write_plug_bio_merged()

Improve blk_zone_write_plug_bio_merged() to check that we succefully get
a reference on the zone write plug 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>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20240501110907.96950-11-dlemoal@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-zoned.c b/block/blk-zoned.c
index cd0049f5bf2ff16c4009bfdaef8962f4b4aaffbd..1890b6d55d8b792a94129ab859420f28195c8e01 100644 (file)
--- a/block/blk-zoned.c
+++ b/block/blk-zoned.c
@@ -885,11 +885,16 @@ 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);