------------[ cut here ]------------
WARNING: CPU: 0 PID: 7980 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: 0 PID: 7980 Comm: syz-executor.2 Not tainted 4.14.232-syzkaller #0
IPVS: ftp: loaded support on port[0] = 21
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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:186
 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:ffff88808c07fb90 EFLAGS: 00010297
RAX: ffff88808c070140 RBX: dffffc0000000000 RCX: ffff88808c07fc00
RDX: 0000000000000000 RSI: ffff88808c0709f0 RDI: ffff88809baff360
RBP: ffff888097d69240 R08: 0000000000000286 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: dead000000000200
R13: dead000000000100 R14: ffff8880907a02c0 R15: ffff888097d692e0
 btrfs_close_devices+0x24/0x140 fs/btrfs/volumes.c:949
 close_ctree+0x38b/0x840 fs/btrfs/disk-io.c:3804
 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: 0033:0x467a37
RSP: 002b:00007ffe2dfa5488 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000467a37
RDX: 00007ffe2dfa555b RSI: 0000000000000002 RDI: 00007ffe2dfa5550
RBP: 00007ffe2dfa5550 R08: 00000000ffffffff R09: 00007ffe2dfa5320
R10: 00000000015d18e3 R11: 0000000000000246 R12: 00000000004bee70
R13: 00007ffe2dfa6620 R14: 00000000015d1810 R15: 00007ffe2dfa6660
Kernel Offset: disabled
Rebooting in 86400 seconds..