linux-kernel - Re: [PATCH] bio: merge_bvec_fn() must be called with the old bi_iter.bi

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Date:	Mon, 11 Aug 2014 16:13:54 +0200
From:	Maurizio Lombardi <mlombard@...hat.com>
To:	axboe@...nel.dk
CC:	linux-kernel@...r.kernel.org, ming.lei@...onical.com,
	jet.chen@...el.com, akpm@...ux-foundation.org,
	Valdis.Kletnieks@...edu
Subject: Re: [PATCH] bio: merge_bvec_fn() must be called with the old bi_iter.bi_size
 value

Hi Jens,

On 07/17/2014 10:49 AM, Maurizio Lombardi wrote:
> The patch "bio: modify __bio_add_page() to accept pages that
> don't start a new segment" updates bio->bi_iter.bi_size before
> calling merge_bvec_fn().
> 
> This panics the kernel because merge_bvec_fn() expects bi_size to have
> the old value.
> 
> This can be reproduced by trying to create a crypto device with cryptsetup.

Can we give to this patch "bio: modify __bio_add_page() to accept pages that don't start a new segment"
another chance to get in?

Should I squash it with the following fix and resubmit as a single patch or it's not necessary?

> 
> Reported-by: Valdis Kletnieks <Valdis.Kletnieks@...edu>
> Signed-off-by: Maurizio Lombardi <mlombard@...hat.com>
> ---
>  block/bio.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block/bio.c b/block/bio.c
> index fb12df9..40c5b12 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -795,7 +795,7 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page
>  		struct bvec_merge_data bvm = {
>  			.bi_bdev = bio->bi_bdev,
>  			.bi_sector = bio->bi_iter.bi_sector,
> -			.bi_size = bio->bi_iter.bi_size,
> +			.bi_size = bio->bi_iter.bi_size - len,
>  			.bi_rw = bio->bi_rw,
>  		};
>  
> 

Thanks,
Maurizio Lombardi
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