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------------[ cut here ]------------
downgrading a read lock
WARNING: CPU: 1 PID: 28014 at kernel/locking/lockdep.c:3556 __lock_downgrade kernel/locking/lockdep.c:3556 [inline]
WARNING: CPU: 1 PID: 28014 at kernel/locking/lockdep.c:3556 lock_downgrade+0x4d7/0x900 kernel/locking/lockdep.c:3819
kobject: 'loop4' (000000004a57d8db): kobject_uevent_env
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 28014 Comm: blkid Not tainted 4.20.0-rc5+ #265
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
kobject: 'loop4' (000000004a57d8db): fill_kobj_path: path = '/devices/virtual/block/loop4'
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x244/0x39d lib/dump_stack.c:113
 panic+0x2ad/0x55c kernel/panic.c:188
kobject: 'loop4' (000000004a57d8db): kobject_uevent_env
 __warn.cold.8+0x20/0x45 kernel/panic.c:540
 report_bug+0x254/0x2d0 lib/bug.c:186
kobject: 'loop4' (000000004a57d8db): fill_kobj_path: path = '/devices/virtual/block/loop4'
 fixup_bug arch/x86/kernel/traps.c:178 [inline]
 do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271
 do_invalid_op+0x36/0x40 arch/x86/kernel/traps.c:290
 invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:969
RIP: 0010:__lock_downgrade kernel/locking/lockdep.c:3556 [inline]
RIP: 0010:lock_downgrade+0x4d7/0x900 kernel/locking/lockdep.c:3819
Code: 00 00 fc ff df 41 c6 44 05 00 f8 e9 1b ff ff ff 48 c7 c7 a0 6d 2b 88 4c 89 9d 58 ff ff ff 48 89 85 60 ff ff ff e8 69 1f e7 ff <0f> 0b 48 8b 85 60 ff ff ff 4c 8d 4d d8 4c 89 e9 48 ba 00 00 00 00
RSP: 0018:ffff88818b09fb70 EFLAGS: 00010086
RAX: 0000000000000000 RBX: 1ffff11031613f74 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff8165fbe5 RDI: 0000000000000006
RBP: ffff88818b09fc28 R08: ffff8881be224700 R09: fffffbfff12b2314
R10: fffffbfff12b2314 R11: ffffffff895918a3 R12: ffffffff8b0f87e0
R13: ffff88818b09fbc0 R14: 0000000000000002 R15: ffff8881be224700
 downgrade_write+0x76/0x270 kernel/locking/rwsem.c:147
 __do_munmap+0xcd8/0xf80 mm/mmap.c:2812
 __vm_munmap+0x138/0x1f0 mm/mmap.c:2837
 __do_sys_munmap mm/mmap.c:2862 [inline]
 __se_sys_munmap mm/mmap.c:2859 [inline]
 __x64_sys_munmap+0x65/0x80 mm/mmap.c:2859
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7f914f01e417
Code: f0 ff ff 73 01 c3 48 8d 0d 8a ad 20 00 31 d2 48 29 c2 89 11 48 83 c8 ff eb eb 90 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 8d 0d 5d ad 20 00 31 d2 48 29 c2 89
RSP: 002b:00007ffe770f16b8 EFLAGS: 00000203 ORIG_RAX: 000000000000000b
RAX: ffffffffffffffda RBX: 00007f914f2291c8 RCX: 00007f914f01e417
RDX: 000000000011f400 RSI: 00000000000033ef RDI: 00007f914f221000
RBP: 00007ffe770f1820 R08: 0000000000000001 R09: 0000000000000007
R10: 00007f914f018a0b R11: 0000000000000203 R12: 0000000094600518
R13: 0000011794600518 R14: 000001179450596e R15: 00007f914f21e740
Kernel Offset: disabled
Rebooting in 86400 seconds..