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Date:   Sun, 12 Apr 2020 00:43:37 +0200
From:   Florian Westphal <fw@strlen.de>
To:     syzbot <syzbot+6ebb6d4830e8f8815623@syzkaller.appspotmail.com>
Cc:     davem@davemloft.net, kuba@kernel.org, linux-kernel@vger.kernel.org,
        mathew.j.martineau@linux.intel.com, matthieu.baerts@tessares.net,
        mptcp@lists.01.org, netdev@vger.kernel.org,
        syzkaller-bugs@googlegroups.com
Subject: Re: [MPTCP] WARNING: bad unlock balance in mptcp_shutdown
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> console output: https://syzkaller.appspot.com/x/log.txt?x=17a5dbfbe00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=ca75979eeebf06c2
> dashboard link: https://syzkaller.appspot.com/bug?extid=6ebb6d4830e8f8815623
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> 
> Unfortunately, I don't have any reproducer for this crash yet.
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+6ebb6d4830e8f8815623@syzkaller.appspotmail.com
> 
> =====================================
> WARNING: bad unlock balance detected!
> 5.6.0-syzkaller #0 Not tainted
> -------------------------------------
> syz-executor.5/2215 is trying to release lock (sk_lock-AF_INET6) at:
> [<ffffffff87c5203b>] mptcp_shutdown+0x38b/0x550 net/mptcp/protocol.c:1889
> but there are no more locks to release!
> 
> other info that might help us debug this:
> 1 lock held by syz-executor.5/2215:
>  #0: ffff88804a22eda0 (slock-AF_INET6){+.-.}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:358 [inline]
>  #0: ffff88804a22eda0 (slock-AF_INET6){+.-.}-{2:2}, at: release_sock+0x1b/0x1b0 net/core/sock.c:2974

I think this is same issue as the other report, so:

#syz dup: WARNING: bad unlock balance in mptcp_poll