Re: [PATCH v2 2/4] dm: Always split write BIOs to zoned device limits

[Christoph Hellwig <hch@infradead.org>]

On Wed, Jun 25, 2025 at 02:59:06PM +0900, Damien Le Moal wrote:
> Any zoned DM target that requires zone append emulation will use the
> block layer zone write plugging. In such case, DM target drivers must
> not split BIOs using dm_accept_partial_bio() as doing so can potentially
> lead to deadlocks with queue freeze operations. Regular write operations
> used to emulate zone append operations also cannot be split by the
> target driver as that would result in an invalid writen sector value
> return using the BIO sector.
> 
> In order for zoned DM target drivers to avoid such incorrect BIO
> splitting, we must ensure that large BIOs are split before being passed
> to the map() function of the target, thus guaranteeing that the
> limits for the mapped device are not exceeded.
> 
> dm-crypt and dm-flakey are the only target drivers supporting zoned
> devices and using dm_accept_partial_bio().

Is there any good way to catch usage dm_accept_partial_bio on zone
devices so that issues like this don't get reintroduced later?