------------[ cut here ]------------
downgrading a read lock
WARNING: CPU: 0 PID: 28644 at kernel/locking/lockdep.c:3553 __lock_downgrade kernel/locking/lockdep.c:3553 [inline]
WARNING: CPU: 0 PID: 28644 at kernel/locking/lockdep.c:3553 lock_downgrade+0x4d2/0x910 kernel/locking/lockdep.c:3816
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 28644 Comm: udevd Not tainted 4.20.0-next-20190107 #6
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+0x1db/0x2d0 lib/dump_stack.c:113
 panic+0x2cb/0x65c kernel/panic.c:214
 __warn.cold+0x20/0x48 kernel/panic.c:571
 report_bug+0x263/0x2b0 lib/bug.c:186
 fixup_bug arch/x86/kernel/traps.c:178 [inline]
 fixup_bug arch/x86/kernel/traps.c:173 [inline]
 do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271
 do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:290
 invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973
RIP: 0010:__lock_downgrade kernel/locking/lockdep.c:3553 [inline]
RIP: 0010:lock_downgrade+0x4d2/0x910 kernel/locking/lockdep.c:3816
Code: 00 00 00 fc ff df 41 c6 04 06 f8 e9 1f ff ff ff 48 c7 c7 c0 a7 4b 88 4c 89 8d 58 ff ff ff 48 89 85 60 ff ff ff e8 fe 13 e7 ff <0f> 0b 48 8b 85 60 ff ff ff 4c 8d 5d d8 4c 89 f1 48 ba 00 00 00 00
RSP: 0018:ffff88808b777bb8 EFLAGS: 00010082
RAX: 0000000000000000 RBX: 1ffff110116eef7d RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff81686376 RDI: 0000000000000006
RBP: ffff88808b777c70 R08: ffff888098f86540 R09: fffffbfff1333299
R10: fffffbfff1333298 R11: ffffffff899994c3 R12: ffff888098f86540
R13: ffffffff8b56ca20 R14: ffff88808b777c08 R15: 0000000000000003
 downgrade_write+0x76/0x270 kernel/locking/rwsem.c:147
 __do_munmap+0xc5a/0xef0 mm/mmap.c:2823
 __vm_munmap+0x139/0x1f0 mm/mmap.c:2848
 __do_sys_munmap mm/mmap.c:2873 [inline]
 __se_sys_munmap mm/mmap.c:2870 [inline]
 __x64_sys_munmap+0x67/0x80 mm/mmap.c:2870
 do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7f578ea28d37
Code: f0 ff ff 73 01 c3 48 8b 0d fe c0 2a 00 31 d2 48 29 c2 64 89 11 48 83 c8 ff eb ea 90 90 90 90 90 90 90 90 b8 0b 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d d1 c0 2a 00 31 d2 48 29 c2 64
RSP: 002b:00007ffe2c166248 EFLAGS: 00000206 ORIG_RAX: 000000000000000b
RAX: ffffffffffffffda RBX: 00000000017f1110 RCX: 00007f578ea28d37
RDX: 0000000000000000 RSI: 0000000000001000 RDI: 00007f578f31f000
RBP: 0000000000000000 R08: 00007f578f3187a0 R09: 0000000000000000
R10: 00000000017f13b0 R11: 0000000000000206 R12: 0000000000000000
R13: 00000000017f1110 R14: 0000000000000006 R15: 0000000000000ae8
Kernel Offset: disabled
Rebooting in 86400 seconds..