Re: [PATCH] block: check bio alignment in blk_mq_submit_bio

[Damien Le Moal <dlemoal@kernel.org>]

On 6/19/24 12:34, Ming Lei wrote:
> IO logical block size is one fundamental queue limit, and every IO has
> to be aligned with logical block size because our bio split can't deal
> with unaligned bio.
> 
> The check has to be done with queue usage counter grabbed because device
> reconfiguration may change logical block size, and we can prevent the
> reconfiguration from happening by holding queue usage counter.
> 
> logical_block_size stays in the 1st cache line of queue_limits, and this
> cache line is always fetched in fast path via bio_may_exceed_limits(),
> so IO perf won't be affected by this check.
> 
> Cc: Yi Zhang <yi.zhang@redhat.com>
> Cc: Christoph Hellwig <hch@infradead.org>
> Cc: Ye Bin <yebin10@huawei.com>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>  block/blk-mq.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 3b4df8e5ac9e..7bb50b6b9567 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -2914,6 +2914,21 @@ static void blk_mq_use_cached_rq(struct request *rq, struct blk_plug *plug,
>  	INIT_LIST_HEAD(&rq->queuelist);
>  }
>  
> +static bool bio_unaligned(const struct bio *bio,
> +		const struct request_queue *q)
> +{
> +	unsigned int bs = queue_logical_block_size(q);
> +
> +	if (bio->bi_iter.bi_size & (bs - 1))
> +		return true;
> +
> +	if (bio->bi_iter.bi_size &&
> +	    ((bio->bi_iter.bi_sector << SECTOR_SHIFT) & (bs - 1)))

Hmmm... Some BIO operations have a 0 size but do specify a sector (e.g. zone
management operations). So this seems incorrect to me...

> +		return true;
> +
> +	return false;
> +}
> +
>  /**
>   * blk_mq_submit_bio - Create and send a request to block device.
>   * @bio: Bio pointer.
> @@ -2966,6 +2981,15 @@ void blk_mq_submit_bio(struct bio *bio)
>  			return;
>  	}
>  
> +	/*
> +	 * Device reconfiguration may change logical block size, so alignment
> +	 * check has to be done with queue usage counter held
> +	 */
> +	if (unlikely(bio_unaligned(bio, q))) {
> +		bio_io_error(bio);
> +		goto queue_exit;
> +	}
> +
>  	if (unlikely(bio_may_exceed_limits(bio, &q->limits))) {
>  		bio = __bio_split_to_limits(bio, &q->limits, &nr_segs);
>  		if (!bio)

-- 
Damien Le Moal
Western Digital Research