[dm-devel] [PATCH 1/3] block: fix blk_rq_get_max_sectors() to flow more carefully

[Damien Le Moal]

On 2020/09/12 6:53, Mike Snitzer wrote:
> blk_queue_get_max_sectors() has been trained for REQ_OP_WRITE_SAME and
> REQ_OP_WRITE_ZEROES yet blk_rq_get_max_sectors() didn't call it for
> those operations.
> 
> Also, there is no need to avoid blk_max_size_offset() if
> 'chunk_sectors' isn't set because it falls back to 'max_sectors'.
> 
> Signed-off-by: Mike Snitzer <snitzer at redhat.com>
> ---
>  include/linux/blkdev.h | 19 +++++++++++++------
>  1 file changed, 13 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index bb5636cc17b9..453a3d735d66 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -1070,17 +1070,24 @@ static inline unsigned int blk_rq_get_max_sectors(struct request *rq,
>  						  sector_t offset)
>  {
>  	struct request_queue *q = rq->q;
> +	int op;
> +	unsigned int max_sectors;
>  
>  	if (blk_rq_is_passthrough(rq))
>  		return q->limits.max_hw_sectors;
>  
> -	if (!q->limits.chunk_sectors ||
> -	    req_op(rq) == REQ_OP_DISCARD ||
> -	    req_op(rq) == REQ_OP_SECURE_ERASE)
> -		return blk_queue_get_max_sectors(q, req_op(rq));
> +	op = req_op(rq);
> +	max_sectors = blk_queue_get_max_sectors(q, op);
>  
> -	return min(blk_max_size_offset(q, offset),
> -			blk_queue_get_max_sectors(q, req_op(rq)));
> +	switch (op) {
> +	case REQ_OP_DISCARD:
> +	case REQ_OP_SECURE_ERASE:
> +	case REQ_OP_WRITE_SAME:
> +	case REQ_OP_WRITE_ZEROES:
> +		return max_sectors;
> +	}

Doesn't this break md devices ? (I think does use chunk_sectors for stride size,
no ?)

As mentioned in my reply to Ming's email, this will allow these commands to
potentially cross over zone boundaries on zoned block devices, which would be an
immediate command failure.

> +
> +	return min(blk_max_size_offset(q, offset), max_sectors);
>  }
>  
>  static inline unsigned int blk_rq_count_bios(struct request *rq)
> 


-- 
Damien Le Moal
Western Digital Research