======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
syz.6.351/6670 is trying to acquire lock:
ffff0000da7ec0b8 (&hdev->lock){+.+.}-{4:4}, at: l2cap_chan_connect+0x84/0xe94 net/bluetooth/l2cap_core.c:7289

but task is already holding lock:
ffff800089eef5a0 (rfcomm_mutex){+.+.}-{4:4}, at: rfcomm_dlc_open+0xa4/0x8b0 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/mutex.c:646 [inline]
       __mutex_lock+0x164/0x1078 kernel/locking/mutex.c:821
       mutex_lock_nested+0x24/0x30 kernel/locking/mutex.c:874
       rfcomm_security_cfm+0x54/0x4c8 net/bluetooth/rfcomm/core.c:2223
       hci_encrypt_cfm+0x30c/0x44c include/net/bluetooth/hci_core.h:2242
       hci_encrypt_change_evt+0x4b4/0xb48 net/bluetooth/hci_event.c:3674
       hci_event_func net/bluetooth/hci_event.c:7887 [inline]
       hci_event_packet+0x4e0/0x9c8 net/bluetooth/hci_event.c:7938
       hci_rx_work+0x2f4/0xd78 net/bluetooth/hci_core.c:4053
       process_one_work kernel/workqueue.c:3396 [inline]
       process_scheduled_works+0x91c/0x1250 kernel/workqueue.c:3479
       worker_thread+0x798/0xbd0 kernel/workqueue.c:3560
       kthread+0x304/0x3d4 kernel/kthread.c:436
       ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:854

-> #1 (hci_cb_list_lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x164/0x1078 kernel/locking/mutex.c:821
       mutex_lock_nested+0x24/0x30 kernel/locking/mutex.c:874
       hci_connect_cfm include/net/bluetooth/hci_core.h:2163 [inline]
       hci_remote_features_evt+0x284/0x5e0 net/bluetooth/hci_event.c:3786
       hci_event_func net/bluetooth/hci_event.c:7887 [inline]
       hci_event_packet+0x4e0/0x9c8 net/bluetooth/hci_event.c:7938
       hci_rx_work+0x2f4/0xd78 net/bluetooth/hci_core.c:4053
       process_one_work kernel/workqueue.c:3396 [inline]
       process_scheduled_works+0x91c/0x1250 kernel/workqueue.c:3479
       worker_thread+0x798/0xbd0 kernel/workqueue.c:3560
       kthread+0x304/0x3d4 kernel/kthread.c:436
       ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:854

-> #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+0x1660/0x2b08 kernel/locking/lockdep.c:5288
       lock_acquire+0x13c/0x320 kernel/locking/lockdep.c:5942
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x164/0x1078 kernel/locking/mutex.c:821
       mutex_lock_nested+0x24/0x30 kernel/locking/mutex.c:874
       l2cap_chan_connect+0x84/0xe94 net/bluetooth/l2cap_core.c:7289
       l2cap_sock_connect+0x44c/0x654 net/bluetooth/l2cap_sock.c:255
       kernel_connect+0x12c/0x1a0 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+0x574/0x8b0 net/bluetooth/rfcomm/core.c:428
       rfcomm_sock_connect+0x278/0x598 net/bluetooth/rfcomm/sock.c:419
       connect_socket net/socket.c:2141 [inline]
       __sys_connect_file+0x13c/0x184 net/socket.c:2166
       __sys_connect+0x114/0x194 net/socket.c:2183
       __do_sys_connect net/socket.c:2189 [inline]
       __se_sys_connect net/socket.c:2186 [inline]
       __arm64_sys_connect+0x84/0x9c net/socket.c:2186
       __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
       invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
       do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
       el0_svc+0x60/0x1d8 arch/arm64/kernel/entry-common.c:796
       el0t_64_sync_handler+0x44/0x104 arch/arm64/kernel/entry-common.c:815
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:606

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.6.351/6670: 1, last CPU#0:
 #0: ffff800089eef5a0 (rfcomm_mutex){+.+.}-{4:4}, at: rfcomm_dlc_open+0xa4/0x8b0 net/bluetooth/rfcomm/core.c:426

stack backtrace:
CPU: 0 UID: 0 PID: 6670 Comm: syz.6.351 Tainted: G             L      syzkaller #0 PREEMPT 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/23/2026
dump_backtrace(regs = 0000000000000000 tsk = 0000000000000000)
Call trace:
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C)
 __dump_stack+0x30/0x40 lib/dump_stack.c:94
 dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120
 dump_stack+0x1c/0x28 lib/dump_stack.c:129
 print_circular_bug+0x328/0x330 kernel/locking/lockdep.c:2087
 check_noncircular+0x158/0x174 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+0x1660/0x2b08 kernel/locking/lockdep.c:5288
 lock_acquire+0x13c/0x320 kernel/locking/lockdep.c:5942
 __mutex_lock_common kernel/locking/mutex.c:646 [inline]
 __mutex_lock+0x164/0x1078 kernel/locking/mutex.c:821
 mutex_lock_nested+0x24/0x30 kernel/locking/mutex.c:874
 l2cap_chan_connect+0x84/0xe94 net/bluetooth/l2cap_core.c:7289
 l2cap_sock_connect+0x44c/0x654 net/bluetooth/l2cap_sock.c:255
 kernel_connect+0x12c/0x1a0 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+0x574/0x8b0 net/bluetooth/rfcomm/core.c:428
 rfcomm_sock_connect+0x278/0x598 net/bluetooth/rfcomm/sock.c:419
 connect_socket net/socket.c:2141 [inline]
 __sys_connect_file+0x13c/0x184 net/socket.c:2166
 __sys_connect+0x114/0x194 net/socket.c:2183
 __do_sys_connect net/socket.c:2189 [inline]
 __se_sys_connect net/socket.c:2186 [inline]
 __arm64_sys_connect+0x84/0x9c net/socket.c:2186
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
 el0_svc+0x60/0x1d8 arch/arm64/kernel/entry-common.c:796
 el0t_64_sync_handler+0x44/0x104 arch/arm64/kernel/entry-common.c:815
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:606