On Thu, 17 Jul 2025, Shin'ichiro Kawasaki wrote:
> Commit 2df7168717b7 ("dm: Always split write BIOs to zoned device
> limits") updates the device-mapper driver to perform splits for the
> write BIOs. However, it did not address the cases where DM targets do
> not emulate zone append, such as in the cases of dm-linear or dm-flakey.
> For these targets, when the write BIOs span across zone boundaries, they
> trigger WARN_ON_ONCE(bio_straddles_zones(bio)) in
> blk_zone_wplug_handle_write(). This results in I/O errors. The errors
> are reproduced by running blktests test case zbd/004 using zoned
> dm-linear or dm-flakey devices.
>
> To avoid the I/O errors, handle the write BIOs regardless whether DM
> targets emulate zone append or not, so that all write BIOs are split at
> zone boundaries. For that purpose, drop the check for zone append
> emulation in dm_zone_bio_needs_split(). Its argument 'md' is no longer
> used then drop it also.
>
> Fixes: 2df7168717b7 ("dm: Always split write BIOs to zoned device limits")
> Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@xxxxxxx>
> Reviewed-by: Damien Le Moal <dlemoal@xxxxxxxxxx>
Reviewed-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> ---
> * Changes from v1:
> - Dropped the first paragraph of the commit message
> - Improved the block comment
>
> drivers/md/dm.c | 18 +++++++-----------
> 1 file changed, 7 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index ca889328fdfe..abfe0392b5a4 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -1785,8 +1785,7 @@ static void init_clone_info(struct clone_info *ci, struct dm_io *io,
> }
>
> #ifdef CONFIG_BLK_DEV_ZONED
> -static inline bool dm_zone_bio_needs_split(struct mapped_device *md,
> - struct bio *bio)
> +static inline bool dm_zone_bio_needs_split(struct bio *bio)
> {
> /*
> * Special case the zone operations that cannot or should not be split.
> @@ -1802,13 +1801,11 @@ static inline bool dm_zone_bio_needs_split(struct mapped_device *md,
> }
>
> /*
> - * Mapped devices that require zone append emulation will use the block
> - * layer zone write plugging. In such case, we must split any large BIO
> - * to the mapped device limits to avoid potential deadlocks with queue
> - * freeze operations.
> + * When mapped devices use the block layer zone write plugging, we must
> + * split any large BIO to the mapped device limits to not submit BIOs
> + * that span zone boundaries and to avoid potential deadlocks with
> + * queue freeze operations.
> */
> - if (!dm_emulate_zone_append(md))
> - return false;
> return bio_needs_zone_write_plugging(bio) || bio_straddles_zones(bio);
> }
>
> @@ -1932,8 +1929,7 @@ static blk_status_t __send_zone_reset_all(struct clone_info *ci)
> }
>
> #else
> -static inline bool dm_zone_bio_needs_split(struct mapped_device *md,
> - struct bio *bio)
> +static inline bool dm_zone_bio_needs_split(struct bio *bio)
> {
> return false;
> }
> @@ -1960,7 +1956,7 @@ static void dm_split_and_process_bio(struct mapped_device *md,
>
> is_abnormal = is_abnormal_io(bio);
> if (static_branch_unlikely(&zoned_enabled)) {
> - need_split = is_abnormal || dm_zone_bio_needs_split(md, bio);
> + need_split = is_abnormal || dm_zone_bio_needs_split(bio);
> } else {
> need_split = is_abnormal;
> }
> --
> 2.50.1
>
