linux-kernel - Re: [PATCH] fs/btrfs: Fix raid6 qstripe kmap'ing

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Message-ID: <20210205153441.GK1993@twin.jikos.cz>
Date:   Fri, 5 Feb 2021 16:34:41 +0100
From:   David Sterba <dsterba@...e.cz>
To:     Ira Weiny <ira.weiny@...el.com>
Cc:     dsterba@...e.cz, clm@...com, josef@...icpanda.com,
        dsterba@...e.com, Miao Xie <miaox@...fujitsu.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] fs/btrfs: Fix raid6 qstripe kmap'ing

On Thu, Feb 04, 2021 at 07:52:36PM -0800, Ira Weiny wrote:
> On Thu, Feb 04, 2021 at 04:26:08PM +0100, David Sterba wrote:
> > On Wed, Feb 03, 2021 at 04:56:48PM +0100, David Sterba wrote:
> > > On Wed, Jan 27, 2021 at 10:15:03PM -0800, ira.weiny@...el.com wrote:
> > > > From: Ira Weiny <ira.weiny@...el.com>
> > > Changelog is good, thanks. I've added stable tags as the missing unmap
> > > is a potential problem.
> > 
> > There are lots of tests faling, stack traces like below. I haven't seen
> > anything obvious in the patch so that needs a closer look and for the
> > time being I can't add the patch to for-next.
> 
> :-(
> 
> I think I may have been off by 1 on the raid6 kmap...
> 
> Something like this should fix it...
> 
> diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c
> index b8a39dad0f00..dbf52f1a379d 100644
> --- a/fs/btrfs/raid56.c
> +++ b/fs/btrfs/raid56.c
> @@ -2370,7 +2370,7 @@ static noinline void finish_parity_scrub(struct btrfs_raid_bio *rbio,
>                         goto cleanup;
>                 }
>                 SetPageUptodate(q_page);
> -               pointers[rbio->real_stripes] = kmap(q_page);
> +               pointers[rbio->real_stripes - 1] = kmap(q_page);

Oh right and tests agree it works.

>         }
>  
>         atomic_set(&rbio->error, 0);
> 
> Let me roll a new version.

No need to, I'll fold the fixup. Thanks.