Re: [PATCHv3 1/8] block: check for valid bio while splitting

[Christoph Hellwig]

On Tue, Aug 19, 2025 at 09:49:15AM -0700, Keith Busch wrote:
>  		/*
>  		 * If the queue doesn't support SG gaps and adding this
>  		 * offset would create a gap, disallow it.
> @@ -339,8 +343,16 @@ int bio_split_rw_at(struct bio *bio, const struct queue_limits *lim,
>  	 * Individual bvecs might not be logical block aligned. Round down the
>  	 * split size so that each bio is properly block size aligned, even if
>  	 * we do not use the full hardware limits.
> +	 *
> +	 * Misuse may submit a bio that can't be split into a valid io. There
> +	 * may either be too many discontiguous vectors for the max segments
> +	 * limit, or contain virtual boundary gaps without having a valid block
> +	 * sized split. Catch that condition by checking for a zero byte
> +	 * result.
>  	 */
>  	bytes = ALIGN_DOWN(bytes, bio_split_alignment(bio, lim));
> +	if (!bytes)

If this is just misuse it could be a WARN_ON_ONCE.  But I think we
can also trigger this when validating passthrough commands that need
to be built to hardware limits.  So maybe don't speak about misuse
here?

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@xxxxxx>