Re: [dm-devel] [PATCH] blk-settings: make sure that max_sectors is aligned on "logical_block_size" boundary. (fwd)

[Ming Lei <ming.lei@redhat.com>]

On Mon, Feb 22, 2021 at 01:15:32PM -0500, Mikulas Patocka wrote:
> 
> 
> ---------- Forwarded message ----------
> Date: Thu, 19 Nov 2020 15:36:51 -0500 (EST)
> From: Mikulas Patocka <mpatocka@redhat.com>
> To: David Teigland <teigland@redhat.com>, Jens Axboe <axboe@kernel.dk>
> Cc: heinzm@redhat.com, Zdenek Kabelac <zkabelac@redhat.com>,
>     Marian Csontos <mcsontos@redhat.com>, linux-block@vger.kernel.org,
>     dm-devel@redhat.com
> Subject: [PATCH] blk-settings: make sure that max_sectors is aligned on
>     "logical_block_size" boundary.
> 
> We get these I/O errors when we run md-raid1 on the top of dm-integrity on 
> the top of ramdisk:
> device-mapper: integrity: Bio not aligned on 8 sectors: 0xff00, 0xff
> device-mapper: integrity: Bio not aligned on 8 sectors: 0xff00, 0xff
> device-mapper: integrity: Bio not aligned on 8 sectors: 0xffff, 0x1
> device-mapper: integrity: Bio not aligned on 8 sectors: 0xffff, 0x1
> device-mapper: integrity: Bio not aligned on 8 sectors: 0x8048, 0xff
> device-mapper: integrity: Bio not aligned on 8 sectors: 0x8147, 0xff
> device-mapper: integrity: Bio not aligned on 8 sectors: 0x8246, 0xff
> device-mapper: integrity: Bio not aligned on 8 sectors: 0x8345, 0xbb
> 
> The ramdisk device has logical_block_size 512 and max_sectors 255. The 
> dm-integrity device uses logical_block_size 4096 and it doesn't affect the 
> "max_sectors" value - thus, it inherits 255 from the ramdisk. So, we have 
> a device with max_sectors not aligned on logical_block_size.
> 
> The md-raid device sees that the underlying leg has max_sectors 255 and it
> will split the bios on 255-sector boundary, making the bios unaligned on
> logical_block_size.
> 
> In order to fix the bug, we round down max_sectors to logical_block_size.
> 
> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> Cc: stable@vger.kernel.org
> 
> ---
>  block/blk-settings.c |   10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> Index: linux-2.6/block/blk-settings.c
> ===================================================================
> --- linux-2.6.orig/block/blk-settings.c	2020-10-29 12:20:46.000000000 +0100
> +++ linux-2.6/block/blk-settings.c	2020-11-19 21:20:18.000000000 +0100
> @@ -591,6 +591,16 @@ int blk_stack_limits(struct queue_limits
>  		ret = -1;
>  	}
>  
> +	t->max_sectors = round_down(t->max_sectors, t->logical_block_size / 512);
> +	if (t->max_sectors < PAGE_SIZE / 512)
> +		t->max_sectors = PAGE_SIZE / 512;
> +	t->max_hw_sectors = round_down(t->max_hw_sectors, t->logical_block_size / 512);
> +	if (t->max_sectors < PAGE_SIZE / 512)

	if (t->max_hw_sectors < PAGE_SIZE / 512)

> +		t->max_hw_sectors = PAGE_SIZE / 512;
> +	t->max_dev_sectors = round_down(t->max_dev_sectors, t->logical_block_size / 512);
> +	if (t->max_sectors < PAGE_SIZE / 512)

	if (t->max_dev_sectors < PAGE_SIZE / 512)

> +		t->max_dev_sectors = PAGE_SIZE / 512;

I'd suggest to add a helper(such as, blk_round_down_sectors()) to round_down each
one.

-- 
Ming

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