linux-kernel - Re: [PATCH v2 8/8] block: add WARN() in bio

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Date:   Thu, 15 Apr 2021 13:00:27 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Satya Tangirala <satyat@...gle.com>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH v2 8/8] block: add WARN() in bio_split() for sector
 alignment

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