Re: [PATCH v2 8/8] block: add WARN() in bio_split() for sector alignment

[Eric Biggers <ebiggers@kernel.org>]

On Thu, Mar 25, 2021 at 09:26:09PM +0000, Satya Tangirala wrote:
> The number of sectors passed to bio_split() should be aligned to
> bio_required_sector_alignment(). All callers (other than bounce.c) have
> been updated to ensure this, so add a WARN() if the number of sectors is
> not aligned. (bounce.c was not updated since it's legacy code that
> won't interact with inline encryption).

What does bounce.c "won't interact with inline encryption" mean, exactly?
Devices that enable bounce buffering won't declare inline encryption support, so
bounce.c will never see a bio that has an encryption context?

> diff --git a/block/bio.c b/block/bio.c
> index 26b7f721cda8..cb348f134a15 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -1458,6 +1458,7 @@ struct bio *bio_split(struct bio *bio, int sectors,
>  
>  	BUG_ON(sectors <= 0);
>  	BUG_ON(sectors >= bio_sectors(bio));
> +	WARN_ON(!IS_ALIGNED(sectors, bio_required_sector_alignment(bio)));

If this warning triggers, shouldn't the function return NULL to indicate a
failure rather than proceeding on?

- Eric