Re: WARNING: locking bug in l2cap_chan_del

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    06a7a37b ipv4: tunnel: fix compilation on ARCH=um
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=115caa16900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=7bb894f55faf8242
dashboard link: https://syzkaller.appspot.com/bug?extid=01d7fc00b2a0419d01cc
compiler:       gcc (GCC) 10.1.0-syz 20200507
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13fb564a900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+01d7fc00b2a0419d01cc@xxxxxxxxxxxxxxxxxxxxxxxxx

------------[ cut here ]------------
DEBUG_LOCKS_WARN_ON(1)
WARNING: CPU: 0 PID: 5 at kernel/locking/lockdep.c:183 hlock_class kernel/locking/lockdep.c:183 [inline]
WARNING: CPU: 0 PID: 5 at kernel/locking/lockdep.c:183 hlock_class kernel/locking/lockdep.c:172 [inline]
WARNING: CPU: 0 PID: 5 at kernel/locking/lockdep.c:183 check_wait_context kernel/locking/lockdep.c:4100 [inline]
WARNING: CPU: 0 PID: 5 at kernel/locking/lockdep.c:183 __lock_acquire+0x1674/0x5640 kernel/locking/lockdep.c:4376
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 5 Comm: kworker/0:0 Not tainted 5.8.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events l2cap_chan_timeout
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x18f/0x20d lib/dump_stack.c:118
 panic+0x2e3/0x75c kernel/panic.c:231
 __warn.cold+0x20/0x45 kernel/panic.c:600
 report_bug+0x1bd/0x210 lib/bug.c:198
 handle_bug+0x38/0x90 arch/x86/kernel/traps.c:235
 exc_invalid_op+0x14/0x40 arch/x86/kernel/traps.c:255
 asm_exc_invalid_op+0x12/0x20 arch/x86/include/asm/idtentry.h:536
RIP: 0010:hlock_class kernel/locking/lockdep.c:183 [inline]
RIP: 0010:hlock_class kernel/locking/lockdep.c:172 [inline]
RIP: 0010:check_wait_context kernel/locking/lockdep.c:4100 [inline]
RIP: 0010:__lock_acquire+0x1674/0x5640 kernel/locking/lockdep.c:4376
Code: d2 0f 85 f1 36 00 00 44 8b 15 f0 8e 57 09 45 85 d2 0f 85 1c fa ff ff 48 c7 c6 80 af 4b 88 48 c7 c7 80 aa 4b 88 e8 ce 36 eb ff <0f> 0b e9 02 fa ff ff c7 44 24 38 fe ff ff ff 41 bf 01 00 00 00 c7
RSP: 0018:ffffc90000cbf8e0 EFLAGS: 00010086
RAX: 0000000000000000 RBX: 0000000000000004 RCX: 0000000000000000
RDX: ffff8880a95a2140 RSI: ffffffff815d8eb7 RDI: fffff52000197f0e
RBP: ffff8880a95a2ab0 R08: 0000000000000000 R09: ffffffff89bcb3c3
R10: 00000000000007d2 R11: 0000000000000001 R12: 0000000000000000
R13: 00000000000019a1 R14: ffff8880a95a2140 R15: 0000000000040000
 lock_acquire+0x1f1/0xad0 kernel/locking/lockdep.c:5005
 __raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline]
 _raw_spin_lock_bh+0x2f/0x40 kernel/locking/spinlock.c:175
 spin_lock_bh include/linux/spinlock.h:359 [inline]
 lock_sock_nested+0x3b/0x110 net/core/sock.c:3040
 l2cap_sock_teardown_cb+0x88/0x400 net/bluetooth/l2cap_sock.c:1520
 l2cap_chan_del+0xad/0x1300 net/bluetooth/l2cap_core.c:618
 l2cap_chan_close+0x118/0xb10 net/bluetooth/l2cap_core.c:823
 l2cap_chan_timeout+0x173/0x450 net/bluetooth/l2cap_core.c:436
 process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
 worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
 kthread+0x3b5/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
Kernel Offset: disabled
Rebooting in 86400 seconds..