Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <000000000000f9136f05c39b84e4@google.com> <21666193-5ad7-2656-c50f-33637fabb082@suse.com>
In-Reply-To: <21666193-5ad7-2656-c50f-33637fabb082@suse.com>
From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Mon, 31 May 2021 10:55:34 +0200
Message-ID: <CACT4Y+bqevMT3cD5sXjSv9QYM_7CwjYmN_Ne5LSj=3-REZ+oTw@mail.gmail.com>
Subject: Re: [syzbot] kernel BUG in assertfail
To:     Nikolay Borisov <nborisov@suse.com>
Cc:     syzbot <syzbot+a6bf271c02e4fe66b4e4@syzkaller.appspotmail.com>,
        Chris Mason <clm@fb.com>, dsterba@suse.com,
        Josef Bacik <josef@toxicpanda.com>,
        linux-btrfs@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Mon, May 31, 2021 at 10:44 AM 'Nikolay Borisov' via syzkaller-bugs
<syzkaller-bugs@googlegroups.com> wrote:
> On 31.05.21 =D0=B3. 10:53, syzbot wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    1434a312 Merge branch 'for-5.13-fixes' of git://git.ker=
nel..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=3D162843f3d00=
000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=3D9f3da44a018=
82e99
> > dashboard link: https://syzkaller.appspot.com/bug?extid=3Da6bf271c02e4f=
e66b4e4
> >
> > Unfortunately, I don't have any reproducer for this issue yet.
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the co=
mmit:
> > Reported-by: syzbot+a6bf271c02e4fe66b4e4@syzkaller.appspotmail.com
> >
> > assertion failed: !memcmp(fs_info->fs_devices->fsid, fs_info->super_cop=
y->fsid, BTRFS_FSID_SIZE), in fs/btrfs/disk-io.c:3282
>
> This means a device contains a btrfs filesystem which has a different
> FSID in its superblock than the fsid which all devices part of the same
> fs_devices should have. This can happen in 2 ways - memory corruption
> where either of the ->fsid member are corrupted or if there was a crash
> while a filesystem's fsid was being changed. We need more context about
> what the test did?

Hi Nikolay,

From a semantic point of view we can consider that it just mounts /dev/rand=
om.
If syzbot comes up with a reproducer it will post it, but you seem to
already figure out what happened, so I assume you can write a unit
test for this.