======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
kworker/u9:5/5602 is trying to acquire lock:
ffffffff8f77b058 (rfcomm_mutex){+.+.}-{4:4}, at: rfcomm_security_cfm+0x90/0x820 net/bluetooth/rfcomm/core.c:2222

but task is already holding lock:
ffffffff8f756998 (hci_cb_list_lock){+.+.}-{4:4}, at: hci_encrypt_cfm+0x313/0x500 include/net/bluetooth/hci_core.h:2239

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (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:2163 [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:4041
       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 (&hdev->lock){+.+.}-{4:4}:
       __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:7281
       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:421
       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

-> #0 (rfcomm_mutex){+.+.}-{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
       rfcomm_security_cfm+0x90/0x820 net/bluetooth/rfcomm/core.c:2222
       hci_encrypt_cfm+0x37e/0x500 include/net/bluetooth/hci_core.h:2242
       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:4041
       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

other info that might help us debug this:

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

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

locks held by kworker/u9:5/5602: 4, last CPU#1:
 #0: ffff8880374ff938 ((wq_completion)hci4#2){+.+.}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:309 [inline]
 #0: ffff8880374ff938 ((wq_completion)hci4#2){+.+.}-{0:0}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
 #0: ffff8880374ff938 ((wq_completion)hci4#2){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3361 [inline]
 #0: ffff8880374ff938 ((wq_completion)hci4#2){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630 kernel/workqueue.c:3479
 #1: ffffc90005997c40 ((work_completion)(&hdev->rx_work)){+.+.}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:309 [inline]
 #1: ffffc90005997c40 ((work_completion)(&hdev->rx_work)){+.+.}-{0:0}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
 #1: ffffc90005997c40 ((work_completion)(&hdev->rx_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3361 [inline]
 #1: ffffc90005997c40 ((work_completion)(&hdev->rx_work)){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630 kernel/workqueue.c:3479
 #2: ffff8880115040b0 (&hdev->lock){+.+.}-{4:4}, at: hci_encrypt_change_evt+0x92/0xcf0 net/bluetooth/hci_event.c:3627
 #3: ffffffff8f756998 (hci_cb_list_lock){+.+.}-{4:4}, at: hci_encrypt_cfm+0x313/0x500 include/net/bluetooth/hci_core.h:2239

stack backtrace:
CPU: 1 UID: 0 PID: 5602 Comm: kworker/u9:5 Tainted: G             L      syzkaller #0 PREEMPT_{RT,(full)} 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: hci4 hci_rx_work
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
 rfcomm_security_cfm+0x90/0x820 net/bluetooth/rfcomm/core.c:2222
 hci_encrypt_cfm+0x37e/0x500 include/net/bluetooth/hci_core.h:2242
 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:4041
 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
 </TASK>