Re: [RESEND PATCH] dm-ebs: Mark full buffer dirty even on partial write

Andrew Morton
2025-10-16T19:59:51Z

On Tue, 14 Oct 2025 16:47:31 +0200 "Uladzislau Rezki (Sony)" <urezki@gmail.com> wrote:

> When performing a read-modify-write(RMW) operation, any modification
> to a buffered block must cause the entire buffer to be marked dirty.
>
> Marking only a subrange as dirty is incorrect because the underlying
> device block size(ubs) defines the minimum read/write granularity. A
> lower device can perform I/O only on regions which are fully aligned
> and sized to ubs.
>
> This change ensures that write-back operations always occur in full
> ubs-sized chunks, matching the intended emulation semantics of the
> EBS target.

It sounds like this can result in corruption under some circumstances?

It would be helpful if you could spell this out clearly, please. What
are the userspace-visible effects of this bug and how are those effects
demonstrated?