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

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Message-Id: <20251016125951.27bb194ab31fe5c61f657a71@linux-foundation.org>
Date: Thu, 16 Oct 2025 12:59:51 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc: Mikulas Patocka <mpatocka@...hat.com>, Alasdair Kergon <agk@...hat.com>,
 Mike Snitzer <snitzer@...hat.com>, Christoph Hellwig <hch@....de>, LKML
 <linux-kernel@...r.kernel.org>, DMML <dm-devel@...ts.linux.dev>
Subject: Re: [RESEND PATCH] dm-ebs: Mark full buffer dirty even on partial
 write

On Tue, 14 Oct 2025 16:47:31 +0200 "Uladzislau Rezki (Sony)" <urezki@...il.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?