Re: [PATCH v2] blk-settings: make sure that max_sectors is aligned on "logical_block_size" boundary

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

On Tue, Feb 23, 2021 at 11:28:27AM -0500, Mikulas Patocka wrote:
> 
> 
> On Tue, 23 Feb 2021, Ming Lei wrote:
> 
> > I'd suggest to add a helper(such as, blk_round_down_sectors()) to round_down each
> > one.
> 
> Yes - Here I'm sending the updated patch.
> 
> > -- 
> > Ming
> 
> From: Mikulas Patocka <mpatocka@redhat.com>
> 
> We get 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 |   12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> Index: linux-2.6/block/blk-settings.c
> ===================================================================
> --- linux-2.6.orig/block/blk-settings.c	2021-02-23 17:18:59.000000000 +0100
> +++ linux-2.6/block/blk-settings.c	2021-02-23 17:23:58.000000000 +0100
> @@ -481,6 +481,14 @@ void blk_queue_io_opt(struct request_que
>  }
>  EXPORT_SYMBOL(blk_queue_io_opt);
>  
> +static unsigned int blk_round_down_sectors(unsigned int sectors, unsigned int lbs)
> +{
> +	sectors = round_down(sectors, lbs >> SECTOR_SHIFT);
> +	if (sectors < PAGE_SIZE >> SECTOR_SHIFT)
> +		sectors = PAGE_SIZE >> SECTOR_SHIFT;
> +	return sectors;
> +}
> +
>  /**
>   * blk_stack_limits - adjust queue_limits for stacked devices
>   * @t:	the stacking driver limits (top device)
> @@ -607,6 +615,10 @@ int blk_stack_limits(struct queue_limits
>  		ret = -1;
>  	}
>  
> +	t->max_sectors = blk_round_down_sectors(t->max_sectors, t->logical_block_size);
> +	t->max_hw_sectors = blk_round_down_sectors(t->max_hw_sectors, t->logical_block_size);
> +	t->max_dev_sectors = blk_round_down_sectors(t->max_dev_sectors, t->logical_block_size);
> +
>  	/* Discard alignment and granularity */
>  	if (b->discard_granularity) {
>  		alignment = queue_limit_discard_alignment(b, start);

Reviewed-by: Ming Lei <ming.lei@redhat.com>

-- 
Ming