From: David Sterba <dsterba@suse.cz>
To: Andrea Righi <andrea.righi@canonical.com>
Cc: Chris Mason <clm@fb.com>, Josef Bacik <josef@toxicpanda.com>,
David Sterba <dsterba@suse.com>,
Johannes Thumshirn <jthumshirn@suse.de>,
linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] btrfs: raid56: properly unmap parity page in finish_parity_scrub()
Date: Mon, 18 Mar 2019 19:47:20 +0100 [thread overview]
Message-ID: <20190318184720.GF3516@twin.jikos.cz> (raw)
In-Reply-To: <20190314075628.GA11282@xps-13>
On Thu, Mar 14, 2019 at 08:56:28AM +0100, Andrea Righi wrote:
> Parity page is incorrectly unmapped in finish_parity_scrub(), triggering
> a reference counter bug on i386, i.e.:
>
> [ 157.662401] kernel BUG at mm/highmem.c:349!
> [ 157.666725] invalid opcode: 0000 [#1] SMP PTI
>
> The reason is that kunmap(p_page) was completely left out, so we never
> did an unmap for the p_page and the loop unmapping the rbio page was
> iterating over the wrong number of stripes: unmapping should be done
> with nr_data instead of rbio->real_stripes.
>
> Test case to reproduce the bug:
>
> - create a raid5 btrfs filesystem:
> # mkfs.btrfs -m raid5 -d raid5 /dev/sdb /dev/sdc /dev/sdd /dev/sde
>
> - mount it:
> # mount /dev/sdb /mnt
>
> - run btrfs scrub in a loop:
> # while :; do btrfs scrub start -BR /mnt; done
>
> BugLink: https://bugs.launchpad.net/bugs/1812845
> Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
> Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Thanks.
prev parent reply other threads:[~2019-03-18 18:46 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-13 10:17 [PATCH] btrfs: raid56: properly unmap parity page in finish_parity_scrub() Andrea Righi
2019-03-13 10:59 ` Johannes Thumshirn
2019-03-14 7:56 ` [PATCH v2] " Andrea Righi
2019-03-18 18:47 ` David Sterba [this message]
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