=====================================
WARNING: bad unlock balance detected!
5.6.0-syzkaller #0 Not tainted
-------------------------------------
syz-executor.4/22009 is trying to release lock (sk_lock-AF_INET6) at:
[<ffffffff87c5f089>] mptcp_poll+0xb9/0x530 net/mptcp/protocol.c:1856
but there are no more locks to release!

other info that might help us debug this:
1 lock held by syz-executor.4/22009:
 #0: ffff888044900de0 (slock-AF_INET6){+.-.}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:358 [inline]
 #0: ffff888044900de0 (slock-AF_INET6){+.-.}-{2:2}, at: release_sock+0x1b/0x1b0 net/core/sock.c:2974

stack backtrace:
CPU: 0 PID: 22009 Comm: syz-executor.4 Not tainted 5.6.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x188/0x20d lib/dump_stack.c:118
 __lock_release kernel/locking/lockdep.c:4633 [inline]
 lock_release+0x586/0x800 kernel/locking/lockdep.c:4941
 sock_release_ownership include/net/sock.h:1539 [inline]
 release_sock+0x177/0x1b0 net/core/sock.c:2984
 mptcp_poll+0xb9/0x530 net/mptcp/protocol.c:1856
 sock_poll+0x15c/0x470 net/socket.c:1271
 vfs_poll include/linux/poll.h:90 [inline]
 do_pollfd fs/select.c:859 [inline]
 do_poll fs/select.c:907 [inline]
 do_sys_poll+0x63c/0xdd0 fs/select.c:1001
 __do_sys_ppoll fs/select.c:1101 [inline]
 __se_sys_ppoll fs/select.c:1081 [inline]
 __x64_sys_ppoll+0x210/0x280 fs/select.c:1081
 do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
 entry_SYSCALL_64_after_hwframe+0x49/0xb3
RIP: 0033:0x45c889
Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f79f7b87c78 EFLAGS: 00000246 ORIG_RAX: 000000000000010f
RAX: ffffffffffffffda RBX: 00007f79f7b886d4 RCX: 000000000045c889
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000020000200
RBP: 000000000076bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000824 R14: 00000000004cadba R15: 000000000076bf0c