linux-kernel - Re: [PATCH] btrfs: scrub: use do

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Message-ID: <20170410111353.GX4781@suse.cz>
Date:   Mon, 10 Apr 2017 13:13:53 +0200
From:   David Sterba <dsterba@...e.cz>
To:     Adam Borowski <kilobyte@...band.pl>
Cc:     Icenowy Zheng <icenowy@...c.io>, Chris Mason <clm@...com>,
        Josef Bacik <jbacik@...com>,
        Fabio Estevam <festevam@...il.com>,
        linux-arm-kernel@...ts.infradead.org, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] btrfs: scrub: use do_div() for 64-by-32 division

On Sat, Apr 08, 2017 at 11:07:37PM +0200, Adam Borowski wrote:
> Unbreaks ARM and possibly other 32-bit architectures.
> 
> Fixes: 7d0ef8b4d: Btrfs: update scrub_parity to use u64 stripe_len
> Reported-by: Icenowy Zheng <icenowy@...c.io>
> Signed-off-by: Adam Borowski <kilobyte@...band.pl>
> ---
> You'd probably want to squash this with Liu's commit, to be nice to future
> bisects.

Thanks for finding it!

> Tested on amd64 where all is fine, and on arm (Odroid-U2) where scrub
> sometimes works, but, like most operations, randomly dies with some badness
> that doesn't look related: io_schedule, kunmap_high.  That badness wasn't
> there in 4.11-rc5, needs investigating, but since it's not connected to our
> issue at hand, I consider this patch sort-of tested.
> 
>  fs/btrfs/scrub.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
> index b6fe1cd08048..95372e3679f3 100644
> --- a/fs/btrfs/scrub.c
> +++ b/fs/btrfs/scrub.c
> @@ -2407,7 +2407,7 @@ static inline void __scrub_mark_bitmap(struct scrub_parity *sparity,
>  
>  	start -= sparity->logic_start;
>  	start = div64_u64_rem(start, sparity->stripe_len, &offset);
> -	offset /= sectorsize;
> +	do_div(offset, sectorsize);

I'll use the div_u64 helper instead, I don't want to reintroduce do_div
to fs/btrfs , for-next will be updated in a minute.