WARNING in __bfs (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 811218ec Linux 4.19.172
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=10fc6a40d00000
kernel config: https://syzkaller.appspot.com/x/.config?x=c1cb1d27398c8808
dashboard link: https://syzkaller.appspot.com/bug?extid=fc86a7c3b2416e6f14fb

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+fc86a7...@syzkaller.appspotmail.com

BTRFS warning (device <unknown>): duplicate device /dev/loop4 devid 1 generation 7 scanned by syz-executor.4 (25617)
BTRFS warning (device <unknown>): duplicate device /dev/loop2 devid 1 generation 7 scanned by systemd-udevd (25599)
BTRFS warning (device <unknown>): duplicate device /dev/loop0 devid 1 generation 7 scanned by systemd-udevd (25328)
------------[ cut here ]------------
WARNING: CPU: 0 PID: 20125 at kernel/locking/lockdep.c:965 lock_accessed kernel/locking/lockdep.c:965 [inline]
WARNING: CPU: 0 PID: 20125 at kernel/locking/lockdep.c:965 __bfs.part.0.cold+0x11/0xeb kernel/locking/lockdep.c:1032
Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 20125 Comm: kworker/0:0 Not tainted 4.19.172-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events l2cap_chan_timeout
Call Trace:
BTRFS warning (device <unknown>): duplicate device /dev/loop0 devid 1 generation 7 scanned by syz-executor.0 (25627)
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1fc/0x2ef lib/dump_stack.c:118
panic+0x26a/0x50e kernel/panic.c:186
__warn.cold+0x20/0x5a kernel/panic.c:541
report_bug+0x262/0x2b0 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+0x1d7/0x310 arch/x86/kernel/traps.c:296
invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:1038
RIP: 0010:lock_accessed kernel/locking/lockdep.c:965 [inline]
RIP: 0010:__bfs.part.0.cold+0x11/0xeb kernel/locking/lockdep.c:1032
Code: 60 b7 23 8d e8 a5 01 a8 f9 eb 88 48 c7 c7 80 75 36 8d e8 97 01 a8 f9 eb bd 48 c7 c7 00 1d 6a 88 48 89 54 24 20 e8 13 87 00 00 <0f> 0b 49 8d 46 10 48 8b 54 24 20 48 89 44 24 18 48 c1 e8 03 42 80
RSP: 0018:ffff88809f227770 EFLAGS: 00010086
RAX: 0000000000000024 RBX: ffffffff8cf87320 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff814de0d1 RDI: ffffed1013e44ee0
RBP: ffff88809f227828 R08: 0000000000000024 R09: 0000000000000000
R10: 0000000000000005 R11: ffffffff8c65d01b R12: ffffffff814a5570
R13: 0000000000000000 R14: 0000000000000000 R15: dffffc0000000000
__bfs kernel/locking/lockdep.c:1387 [inline]
__bfs_backwards kernel/locking/lockdep.c:1069 [inline]
find_usage_backwards kernel/locking/lockdep.c:1387 [inline]
check_usage_backwards+0x17a/0x300 kernel/locking/lockdep.c:2668
mark_lock_irq kernel/locking/lockdep.c:2759 [inline]
mark_lock+0x3d8/0x1160 kernel/locking/lockdep.c:3131
mark_irqflags kernel/locking/lockdep.c:3023 [inline]
__lock_acquire+0x63f/0x3ff0 kernel/locking/lockdep.c:3372
lock_acquire+0x170/0x3c0 kernel/locking/lockdep.c:3907
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline]
_raw_spin_lock_bh+0x2f/0x40 kernel/locking/spinlock.c:168
spin_lock_bh include/linux/spinlock.h:334 [inline]
lock_sock_nested+0x3b/0x110 net/core/sock.c:2864
l2cap_sock_teardown_cb+0xa0/0x6d0 net/bluetooth/l2cap_sock.c:1340
l2cap_chan_del+0xbc/0xa50 net/bluetooth/l2cap_core.c:599
l2cap_chan_close+0x1b5/0x950 net/bluetooth/l2cap_core.c:757
l2cap_chan_timeout+0x17e/0x2f0 net/bluetooth/l2cap_core.c:430
process_one_work+0x864/0x1570 kernel/workqueue.c:2155
worker_thread+0x64c/0x1130 kernel/workqueue.c:2298
kthread+0x33f/0x460 kernel/kthread.c:259
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415
Shutting down cpus with NMI
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.