Re: [PATCH] block: Split bios in LBA order

[Christoph Hellwig <hch@lst.de>]

On Mon, May 12, 2025 at 03:56:23PM -0700, Bart Van Assche wrote:
> The block layer submits bio fragments in opposite LBA order. Fix this as
> follows:
> - Introduce a new function bio_split_to_limits_and_submit() that has the
>   same behavior as the existing bio_split_to_limits() function. This
>   involves splitting a bio and submitting the fragment with the highest
>   LBA by calling submit_bio_noacct().
> - Use the new function bio_split_to_limits_and_submit() in all drivers
>   that are fine with submitting split bios in opposite LBA order.

If you have to rename a user visible symbol, please do that in a
preparation patch.

Also how do you determine some drivers are fine with one order while
others are not?

> - Modify blk_mq_submit_bio() and dm_split_and_process_bio() such that
>   bio fragments are submitted in LBA order.

blk_mq_submit_bio calls __bio_split_to_limits, which returns the
bio split off the beginning of the passed in bio by bio_submit_split.
I don't see how that would reorder anything.