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WARNING: CPU: 1 PID: 7971 at fs/btrfs/volumes.c:936 __btrfs_close_devices+0x888/0xb20 fs/btrfs/volumes.c:936
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 7971 Comm: syz-executor.5 Not tainted 4.14.289-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/29/2022
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x1b2/0x281 lib/dump_stack.c:58
 panic+0x1f9/0x42d kernel/panic.c:183
 __warn.cold+0x20/0x44 kernel/panic.c:547
 report_bug+0x208/0x250 lib/bug.c:183
 fixup_bug arch/x86/kernel/traps.c:177 [inline]
 fixup_bug arch/x86/kernel/traps.c:172 [inline]
 do_error_trap+0x195/0x2d0 arch/x86/kernel/traps.c:295
 invalid_op+0x1b/0x40 arch/x86/entry/entry_64.S:964
RIP: 0010:__btrfs_close_devices+0x888/0xb20 fs/btrfs/volumes.c:936
RSP: 0018:ffff8880b1b17b90 EFLAGS: 00010297
l2tp_core: tunl 0: fd 6 wrong protocol, got 17, expected 115
RAX: ffff8880a53f4040 RBX: dffffc0000000000 RCX: ffff8880b1b17c00
RDX: 0000000000000000 RSI: ffff8880a53f48f0 RDI: ffff8880aa0442e0
RBP: ffff8880a98cfb00 R08: 0000000000000286 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: dead000000000200
R13: dead000000000100 R14: ffff8880b1ded6c0 R15: ffff8880a98cfba0
 btrfs_close_devices+0x24/0x140 fs/btrfs/volumes.c:949
 close_ctree+0x38b/0x840 fs/btrfs/disk-io.c:3816
 generic_shutdown_super+0x144/0x370 fs/super.c:446
 kill_anon_super+0x36/0x90 fs/super.c:1006
 btrfs_kill_super+0x49/0x540 fs/btrfs/super.c:2163
 deactivate_locked_super+0x6c/0xd0 fs/super.c:319
 deactivate_super+0x7f/0xa0 fs/super.c:350
 cleanup_mnt+0x186/0x2c0 fs/namespace.c:1183
 task_work_run+0x11f/0x190 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 exit_to_usermode_loop+0x1ad/0x200 arch/x86/entry/common.c:164
 prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:270 [inline]
 do_syscall_64+0x4a3/0x640 arch/x86/entry/common.c:297
 entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x7f5a55e1d677
RSP: 002b:00007ffc3d3fe2b8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 00007f5a55e1d677
RDX: 00007ffc3d3fe389 RSI: 000000000000000a RDI: 00007ffc3d3fe380
RBP: 00007ffc3d3fe380 R08: 00000000ffffffff R09: 00007ffc3d3fe150
l2tp_core: tunl 0: fd 6 wrong protocol, got 17, expected 115
R10: 0000555555cd7903 R11: 0000000000000246 R12: 00007f5a55e752a6
R13: 00007ffc3d3ff440 R14: 0000555555cd7810 R15: 00007ffc3d3ff480
Kernel Offset: disabled
Rebooting in 86400 seconds..