On 2025/07/17 11:32, Shin'ichiro Kawasaki wrote:
> Since commit f70291411ba2 ("block: Introduce
> bio_needs_zone_write_plugging()"), blk_mq_submit_bio() no longer splits
> write BIOs to comply with the requirements of zoned block devices. This
> change applies to write BIOs issued by zoned DM targets. Following this
> modification, it is expected that DM targets themselves split write BIOs
> for zoned block devices.
This description is confusing: if the underlying device of a DM target is a
blk-mq block device, then blk_mq_submit_bio() will be called and will split BIOs
as needed, regardless of what the DM target did. For BIOs that are issued by the
user/FS to the DM device, then that is when bio_needs_zone_write_plugging() is
used by DM core to determine if a BIO must be split.
Anyway, I do not think you need to reference this commit. So I would drop this
entire paragraph from the commit message, and start the explanation with the
below paragraph. That is very clear I think.
> 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")
> Cc: [email protected]
The above patch is queued in block-next, so there is no need for this CC-stable.
Remove it please.
> Signed-off-by: Shin'ichiro Kawasaki <[email protected]>
One more nit below.
With these fixed, feel free to add:
Reviewed-by: Damien Le Moal <[email protected]>
> ---
> drivers/md/dm.c | 17 ++++++-----------
> 1 file changed, 6 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index ca889328fdfe..a64809f04241 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 +1801,10 @@ 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 avoid potential
> + * deadlocks with queue freeze operations.
Nit:
* 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 +1928,7 @@ 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 +1955,7 @@ 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;
> }
--
Damien Le Moal
Western Digital Research
