Re: [PATCH v2 3/5] btrfs: scrub: Don't append on-disk pages for raid56 scrub

From: Liu Bo <bo.li.liu@oracle.com>
To: Qu Wenruo <quwenruo@cn.fujitsu.com>
Cc: linux-btrfs@vger.kernel.org
Subject: Re: [PATCH v2 3/5] btrfs: scrub: Don't append on-disk pages for raid56 scrub
Date: Fri, 24 Mar 2017 15:06:18 -0700	[thread overview]
Message-ID: <20170324220618.GA26987@lim.localdomain> (raw)
In-Reply-To: <20170324020027.21228-4-quwenruo@cn.fujitsu.com>

On Fri, Mar 24, 2017 at 10:00:25AM +0800, Qu Wenruo wrote:
> In the following situation, scrub will calculate wrong parity to
> overwrite correct one:
> 
> RAID5 full stripe:
> 
> Before
> |     Dev 1      |     Dev  2     |     Dev 3     |
> | Data stripe 1  | Data stripe 2  | Parity Stripe |
> --------------------------------------------------- 0
> | 0x0000 (Bad)   |     0xcdcd     |     0x0000    |
> --------------------------------------------------- 4K
> |     0xcdcd     |     0xcdcd     |     0x0000    |
> ...
> |     0xcdcd     |     0xcdcd     |     0x0000    |
> --------------------------------------------------- 64K
> 
> After scrubbing dev3 only:
> 
> |     Dev 1      |     Dev  2     |     Dev 3     |
> | Data stripe 1  | Data stripe 2  | Parity Stripe |
> --------------------------------------------------- 0
> | 0xcdcd (Good)  |     0xcdcd     | 0xcdcd (Bad)  |
> --------------------------------------------------- 4K
> |     0xcdcd     |     0xcdcd     |     0x0000    |
> ...
> |     0xcdcd     |     0xcdcd     |     0x0000    |
> --------------------------------------------------- 64K
> 
> The reason is after raid56 read rebuild rbio->stripe_pages are all
> correct recovered (0xcd for data stripes).
> 
> However when we check and repair parity, in
> scrub_parity_check_and_repair(), we will appending pages in
> sparity->spages list to rbio->bio_pages[], which contains old on-disk
> data.
> 
> And when we submit parity data to disk, we calculate parity using
> rbio->bio_pages[] first, if rbio->bio_pages[] not found, then fallback
> to rbio->stripe_pages[].
> 
> The patch fix it by not appending pages from sparity->spages.
> So finish_parity_scrub() will use rbio->stripe_pages[] which is correct.

Reviewed-by: Liu Bo <bo.li.liu@oracle.com>

Thanks,

-liubo
> 
> Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
> ---
>  fs/btrfs/scrub.c | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
> index 6832feece7a7..2a5458004279 100644
> --- a/fs/btrfs/scrub.c
> +++ b/fs/btrfs/scrub.c
> @@ -2957,7 +2957,6 @@ static void scrub_parity_check_and_repair(struct scrub_parity *sparity)
>  	struct btrfs_fs_info *fs_info = sctx->fs_info;
>  	struct bio *bio;
>  	struct btrfs_raid_bio *rbio;
> -	struct scrub_page *spage;
>  	struct btrfs_bio *bbio = NULL;
>  	u64 length;
>  	int ret;
> @@ -2987,9 +2986,6 @@ static void scrub_parity_check_and_repair(struct scrub_parity *sparity)
>  	if (!rbio)
>  		goto rbio_out;
>  
> -	list_for_each_entry(spage, &sparity->spages, list)
> -		raid56_add_scrub_pages(rbio, spage->page, spage->logical);
> -
>  	scrub_pending_bio_inc(sctx);
>  	raid56_parity_submit_scrub_rbio(rbio);
>  	return;
> -- 
> 2.12.1
> 
> 
>