linux-kernel - Re: [PATCH] dm-bufio: align write boundary on bdev_logical_block

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Message-ID: <aQCDLBie3fGwMDW2@milan>
Date: Tue, 28 Oct 2025 09:47:40 +0100
From: Uladzislau Rezki <urezki@...il.com>
To: Mikulas Patocka <mpatocka@...hat.com>
Cc: "Uladzislau Rezki (Sony)" <urezki@...il.com>,
	Alasdair Kergon <agk@...hat.com>, DMML <dm-devel@...ts.linux.dev>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Snitzer <snitzer@...hat.com>, Christoph Hellwig <hch@....de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] dm-bufio: align write boundary on bdev_logical_block_size

Hello!

Sorry i have missed you email for unknown reason to me. It is
probably because you answered to email with different subject
i sent initially.

> 
> On Mon, 20 Oct 2025, Uladzislau Rezki (Sony) 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.
> 
> Hi
> 
> I think it would be better to fix this in dm-bufio, so that other dm-bufio 
> users would also benefit from the fix. Please try this patch - does it fix 
> it?
> 
If it solves what i describe i do not mind :)

> 
> 
> From: Mikulas Patocka <mpatocka@...hat.com>
> 
> There may be devices with logical block size larger than 4k. Fix
> dm-bufio, so that it will align I/O on logical block size. This commit
> fixes I/O errors on the dm-ebs target on the top of emulated nvme device
> with 8k logical block size created with qemu parameters:
> 
> -device nvme,drive=drv0,serial=foo,logical_block_size=8192,physical_block_size=8192
> 
> Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>
> Cc: stable@...r.kernel.org
> 
> ---
>  drivers/md/dm-bufio.c |    9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> Index: linux-2.6/drivers/md/dm-bufio.c
> ===================================================================
> --- linux-2.6.orig/drivers/md/dm-bufio.c	2025-10-13 21:42:47.000000000 +0200
> +++ linux-2.6/drivers/md/dm-bufio.c	2025-10-20 14:40:32.000000000 +0200
> @@ -1374,7 +1374,7 @@ static void submit_io(struct dm_buffer *
>  {
>  	unsigned int n_sectors;
>  	sector_t sector;
> -	unsigned int offset, end;
> +	unsigned int offset, end, align;
>  
>  	b->end_io = end_io;
>  
> @@ -1388,9 +1388,10 @@ static void submit_io(struct dm_buffer *
>  			b->c->write_callback(b);
>  		offset = b->write_start;
>  		end = b->write_end;
> -		offset &= -DM_BUFIO_WRITE_ALIGN;
> -		end += DM_BUFIO_WRITE_ALIGN - 1;
> -		end &= -DM_BUFIO_WRITE_ALIGN;
> +		align = max(DM_BUFIO_WRITE_ALIGN, bdev_logical_block_size(b->c->bdev));
> +		offset &= -align;
> +		end += align - 1;
> +		end &= -align;
>  		if (unlikely(end > b->c->block_size))
>  			end = b->c->block_size;
>  
> 
I will check it and get back soon.

Thank you.

--
Uladzislau Rezki