Re: [PATCH 2/2] md: raid1: use bio_rewind() before bio_copy_data()

[NeilBrown <neilb@suse.de>]

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On Mon,  8 Jul 2013 16:25:14 -0400 Joe Lawrence <joe.lawrence@stratus.com>
wrote:

> bio_copy_data() cannot execute on a fully completed source (or
> destination) bio.  MD RAID1 is recycling a completed read bio for RAID
> repair purposes and needs to fix up the source and destination bios for
> bio_copy_data(): in particular, the io-vector index needs to be rewound
> and the bios unchained.
> 
> Suggested-by: NeilBrown <neilb@suse.de>
> Signed-off-by: Joe Lawrence <joe.lawrence@stratus.com>

Thanks Joe.

Jens:  are you happy with this?  If so is it OK for me to forward to Linus
and -stable for 3.10, or would you rather?
The follow-on patch which uses the so avoid a crash is 

http://marc.info/?l=linux-raid&m=137331514131503&w=2

(This is sitting near the top of "git://neil.brown.name/md for-next" if you
want to cherry-pick it).

Thanks,
NeilBrown

> ---
>  drivers/md/raid1.c | 28 +++++-----------------------
>  1 file changed, 5 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index 6e17f81..bb1e80f 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
> @@ -1861,7 +1861,6 @@ static int process_checks(struct r1bio *r1_bio)
>  		int j;
>  		struct bio *pbio = r1_bio->bios[primary];
>  		struct bio *sbio = r1_bio->bios[i];
> -		int size;
>  
>  		if (sbio->bi_end_io != end_sync_read)
>  			continue;
> @@ -1887,28 +1886,11 @@ static int process_checks(struct r1bio *r1_bio)
>  			rdev_dec_pending(conf->mirrors[i].rdev, mddev);
>  			continue;
>  		}
> -		/* fixup the bio for reuse */
> -		bio_reset(sbio);
> -		sbio->bi_vcnt = vcnt;
> -		sbio->bi_size = r1_bio->sectors << 9;
> -		sbio->bi_sector = r1_bio->sector +
> -			conf->mirrors[i].rdev->data_offset;
> -		sbio->bi_bdev = conf->mirrors[i].rdev->bdev;
> -		sbio->bi_end_io = end_sync_read;
> -		sbio->bi_private = r1_bio;
> -
> -		size = sbio->bi_size;
> -		for (j = 0; j < vcnt ; j++) {
> -			struct bio_vec *bi;
> -			bi = &sbio->bi_io_vec[j];
> -			bi->bv_offset = 0;
> -			if (size > PAGE_SIZE)
> -				bi->bv_len = PAGE_SIZE;
> -			else
> -				bi->bv_len = size;
> -			size -= PAGE_SIZE;
> -		}
> -
> +		/* copy pbio io_vec data into sbio, but first reset io_vec
> +		 * index and unchain both */
> +		bio_rewind(pbio);
> +		bio_rewind(sbio);
> +		pbio->bi_next = sbio->bi_next = NULL;
>  		bio_copy_data(sbio, pbio);
>  	}
>  	return 0;


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