00:00:00:00:00:00 -> 12:aa:aa:aa:aa:aa
hci6 orig refcnt 14
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
syz.1.836/9321 is trying to acquire lock:
ffff88804d6280b0 (&hdev->lock){+.+.}-{4:4}, at: l2cap_chan_connect+0x9c/0x1110 net/bluetooth/l2cap_core.c:7289

but task is already holding lock:
ffffffff8f77dbd8 (rfcomm_mutex){+.+.}-{4:4}, at: rfcomm_dlc_open+0x9c/0x1080 net/bluetooth/rfcomm/core.c:426

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (rfcomm_mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/rtmutex_api.c:561 [inline]
       mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:580
       rfcomm_security_cfm+0x90/0x820 net/bluetooth/rfcomm/core.c:2223
       hci_encrypt_cfm+0x37e/0x500 include/net/bluetooth/hci_core.h:2243
       hci_encrypt_change_evt+0x5db/0xcf0 net/bluetooth/hci_event.c:3674
       hci_event_func net/bluetooth/hci_event.c:7887 [inline]
       hci_event_packet+0x6cd/0xf10 net/bluetooth/hci_event.c:7938
       hci_rx_work+0x3ee/0x1020 net/bluetooth/hci_core.c:4087
       process_one_work kernel/workqueue.c:3396 [inline]
       process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3479
       worker_thread+0xa47/0xfb0 kernel/workqueue.c:3560
       kthread+0x38b/0x470 kernel/kthread.c:436
       ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #1 (hci_cb_list_lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/rtmutex_api.c:561 [inline]
       mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:580
       hci_connect_cfm include/net/bluetooth/hci_core.h:2164 [inline]
       hci_remote_features_evt+0x53d/0x950 net/bluetooth/hci_event.c:3786
       hci_event_func net/bluetooth/hci_event.c:7887 [inline]
       hci_event_packet+0x6cd/0xf10 net/bluetooth/hci_event.c:7938
       hci_rx_work+0x3ee/0x1020 net/bluetooth/hci_core.c:4087
       process_one_work kernel/workqueue.c:3396 [inline]
       process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3479
       worker_thread+0xa47/0xfb0 kernel/workqueue.c:3560
       kthread+0x38b/0x470 kernel/kthread.c:436
       ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #0 (&hdev->lock){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3209 [inline]
       check_prevs_add kernel/locking/lockdep.c:3328 [inline]
       validate_chain kernel/locking/lockdep.c:3952 [inline]
       __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
       lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
       __mutex_lock_common kernel/locking/rtmutex_api.c:561 [inline]
       mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:580
       l2cap_chan_connect+0x9c/0x1110 net/bluetooth/l2cap_core.c:7289
       l2cap_sock_connect+0x5e4/0x7e0 net/bluetooth/l2cap_sock.c:255
       kernel_connect+0x141/0x1c0 net/socket.c:3755
       rfcomm_session_create net/bluetooth/rfcomm/core.c:808 [inline]
       __rfcomm_dlc_open net/bluetooth/rfcomm/core.c:385 [inline]
       rfcomm_dlc_open+0x644/0x1080 net/bluetooth/rfcomm/core.c:428
       rfcomm_sock_connect+0x2ed/0x650 net/bluetooth/rfcomm/sock.c:419
       connect_socket net/socket.c:2141 [inline]
       __sys_connect_file net/socket.c:2166 [inline]
       __sys_connect+0x32d/0x470 net/socket.c:2183
       __do_sys_connect net/socket.c:2189 [inline]
       __se_sys_connect net/socket.c:2186 [inline]
       __x64_sys_connect+0x7a/0x90 net/socket.c:2186
       do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
       do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  &hdev->lock --> hci_cb_list_lock --> rfcomm_mutex

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(rfcomm_mutex);
                               lock(hci_cb_list_lock);
                               lock(rfcomm_mutex);
  lock(&hdev->lock);

 *** DEADLOCK ***

locks held by syz.1.836/9321: 1, last CPU#1:
 #0: ffffffff8f77dbd8 (rfcomm_mutex){+.+.}-{4:4}, at: rfcomm_dlc_open+0x9c/0x1080 net/bluetooth/rfcomm/core.c:426

stack backtrace:
CPU: 1 UID: 0 PID: 9321 Comm: syz.1.836 Tainted: G             L      syzkaller #0 PREEMPT_{RT,(full)} 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2087
 check_noncircular+0x12f/0x150 kernel/locking/lockdep.c:2219
 check_prev_add kernel/locking/lockdep.c:3209 [inline]
 check_prevs_add kernel/locking/lockdep.c:3328 [inline]
 validate_chain kernel/locking/lockdep.c:3952 [inline]
 __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
 __mutex_lock_common kernel/locking/rtmutex_api.c:561 [inline]
 mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:580
 l2cap_chan_connect+0x9c/0x1110 net/bluetooth/l2cap_core.c:7289
 l2cap_sock_connect+0x5e4/0x7e0 net/bluetooth/l2cap_sock.c:255
 kernel_connect+0x141/0x1c0 net/socket.c:3755
 rfcomm_session_create net/bluetooth/rfcomm/core.c:808 [inline]
 __rfcomm_dlc_open net/bluetooth/rfcomm/core.c:385 [inline]
 rfcomm_dlc_open+0x644/0x1080 net/bluetooth/rfcomm/core.c:428
 rfcomm_sock_connect+0x2ed/0x650 net/bluetooth/rfcomm/sock.c:419
 connect_socket net/socket.c:2141 [inline]
 __sys_connect_file net/socket.c:2166 [inline]
 __sys_connect+0x32d/0x470 net/socket.c:2183
 __do_sys_connect net/socket.c:2189 [inline]
 __se_sys_connect net/socket.c:2186 [inline]
 __x64_sys_connect+0x7a/0x90 net/socket.c:2186
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fea949de199
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fea92c36028 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 00007fea94c65fa0 RCX: 00007fea949de199
RDX: 000000000000000a RSI: 0000200000000040 RDI: 0000000000000004
RBP: 00007fea94a758e0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fea94c66038 R14: 00007fea94c65fa0 R15: 00007ffd56bae938
 </TASK>