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@linux.ibm.com>
Signed-off-by: John Garry <john.g.garry@oracle.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;
+	}
+
 	boundary_sectors = lim->atomic_write_hw_boundary >> SECTOR_SHIFT;
 
 	if (boundary_sectors) {
-- 
2.43.5

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@linux.ibm.com>
> Signed-off-by: John Garry <john.g.garry@oracle.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

On 10/07/2025 16:08, Jens Axboe wrote:
>> +	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.

ok, I can tidy that up.

Thanks,
John