linux-kernel - Re: [PATCH v5 2/6] block: sanitize chunk

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Message-ID: <04620cc5-7c3a-4e4f-87ce-b691d9b57917@kernel.dk>
Date: Thu, 10 Jul 2025 09:08:44 -0600
From: Jens Axboe <axboe@...nel.dk>
To: John Garry <john.g.garry@...cle.com>, agk@...hat.com, snitzer@...nel.org,
 mpatocka@...hat.com, song@...nel.org, yukuai3@...wei.com, hch@....de,
 nilay@...ux.ibm.com, cem@...nel.org
Cc: dm-devel@...ts.linux.dev, linux-kernel@...r.kernel.org,
 linux-raid@...r.kernel.org, linux-block@...r.kernel.org,
 ojaswin@...ux.ibm.com, martin.petersen@...cle.com,
 akpm@...ux-foundation.org, linux-xfs@...r.kernel.org, djwong@...nel.org
Subject: Re: [PATCH v5 2/6] block: sanitize chunk_sectors for atomic write
 limits

On 7/9/25 4:02 AM, John Garry wrote:
> Currently we just ensure that a non-zero value in chunk_sectors aligns
> with any atomic write boundary, as the blk boundary functionality uses
> both these values.
> 
> However it is also improper to have atomic write unit max > chunk_sectors
> (for non-zero chunk_sectors), as this would lead to splitting of atomic
> write bios (which is disallowed).
> 
> Sanitize atomic write unit max against chunk_sectors to avoid any
> potential problems.
> 
> Fixes: d00eea91deaf3 ("block: Add extra checks in blk_validate_atomic_write_limits()")
> Reviewed-by: Nilay Shroff <nilay@...ux.ibm.com>
> Signed-off-by: John Garry <john.g.garry@...cle.com>
> ---
>  block/blk-settings.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/block/blk-settings.c b/block/blk-settings.c
> index a000daafbfb4..725035376f51 100644
> --- a/block/blk-settings.c
> +++ b/block/blk-settings.c
> @@ -180,6 +180,7 @@ static void blk_atomic_writes_update_limits(struct queue_limits *lim)
>  
>  static void blk_validate_atomic_write_limits(struct queue_limits *lim)
>  {
> +	unsigned long long chunk_bytes;
>  	unsigned int boundary_sectors;
>  
>  	if (!(lim->features & BLK_FEAT_ATOMIC_WRITES))
> @@ -202,6 +203,13 @@ static void blk_validate_atomic_write_limits(struct queue_limits *lim)
>  			 lim->atomic_write_hw_max))
>  		goto unsupported;
>  
> +	chunk_bytes = lim->chunk_sectors << SECTOR_SHIFT;
> +	if (chunk_bytes) {
> +		if (WARN_ON_ONCE(lim->atomic_write_hw_unit_max >
> +			chunk_bytes))
> +			goto unsupported;
> +	}

Unnecessary indentation here. Why not just:

	chunk_bytes = lim->chunk_sectors << SECTOR_SHIFT;
	if (WARN_ON_ONCE(chunk_bytes &&
			 lim->atomic_write_hw_unit_max > chunk_bytes))
		goto unsupposed.

Also avoids splitting a comparison over multiple lines, which is always
annoying to read.

-- 
Jens Axboe