======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
kworker/u9:0/53 is trying to acquire lock:
ffff0000de46e040 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: touch_work_lockdep_map+0x70/0x118 kernel/workqueue.c:3949

but task is already holding lock:
ffff0000de46e338 (&conn->lock#2){+.+.}-{4:4}, at: l2cap_conn_del+0x74/0x5f0 net/bluetooth/l2cap_core.c:1762

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&conn->lock#2){+.+.}-{4:4}:
       __mutex_lock_common+0x1d0/0x2678 kernel/locking/mutex.c:598
       __mutex_lock kernel/locking/mutex.c:760 [inline]
       mutex_lock_nested+0x2c/0x38 kernel/locking/mutex.c:812
       l2cap_info_timeout+0x70/0xb0 net/bluetooth/l2cap_core.c:1668
       process_one_work+0x7e8/0x155c kernel/workqueue.c:3263
       process_scheduled_works kernel/workqueue.c:3346 [inline]
       worker_thread+0x958/0xed8 kernel/workqueue.c:3427
       kthread+0x5fc/0x75c kernel/kthread.c:463
       ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844

-> #0 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x1774/0x30a4 kernel/locking/lockdep.c:5237
       lock_acquire+0x14c/0x2e0 kernel/locking/lockdep.c:5868
       touch_work_lockdep_map+0x98/0x118 kernel/workqueue.c:3951
       start_flush_work kernel/workqueue.c:4205 [inline]
       __flush_work+0x4fc/0x8c0 kernel/workqueue.c:4237
       __cancel_work_sync kernel/workqueue.c:4393 [inline]
       cancel_delayed_work_sync+0xc4/0x120 kernel/workqueue.c:4467
       l2cap_conn_del+0x460/0x5f0 net/bluetooth/l2cap_core.c:1796
       l2cap_disconn_cfm+0x90/0xe0 net/bluetooth/l2cap_core.c:7325
       hci_disconn_cfm include/net/bluetooth/hci_core.h:2121 [inline]
       hci_disconn_complete_evt+0x424/0x830 net/bluetooth/hci_event.c:3433
       hci_event_func net/bluetooth/hci_event.c:7559 [inline]
       hci_event_packet+0x704/0xf04 net/bluetooth/hci_event.c:7613
       hci_rx_work+0x320/0xb18 net/bluetooth/hci_core.c:4099
       process_one_work+0x7e8/0x155c kernel/workqueue.c:3263
       process_scheduled_works kernel/workqueue.c:3346 [inline]
       worker_thread+0x958/0xed8 kernel/workqueue.c:3427
       kthread+0x5fc/0x75c kernel/kthread.c:463
       ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&conn->lock#2);
                               lock((work_completion)(&(&conn->info_timer)->work));
                               lock(&conn->lock#2);
  lock((work_completion)(&(&conn->info_timer)->work));

 *** DEADLOCK ***

6 locks held by kworker/u9:0/53:
 #0: ffff0000cc68b148 ((wq_completion)hci4#2){+.+.}-{0:0}, at: process_one_work+0x63c/0x155c kernel/workqueue.c:3237
 #1: ffff8000991c7be0 ((work_completion)(&hdev->rx_work)){+.+.}-{0:0}, at: process_one_work+0x6d4/0x155c kernel/workqueue.c:3237
 #2: ffff0000cc65c0b8 (&hdev->lock){+.+.}-{4:4}, at: hci_disconn_complete_evt+0x4c/0x830 net/bluetooth/hci_event.c:3375
 #3: ffff8000929c3c08 (hci_cb_list_lock){+.+.}-{4:4}, at: hci_disconn_cfm include/net/bluetooth/hci_core.h:2118 [inline]
 #3: ffff8000929c3c08 (hci_cb_list_lock){+.+.}-{4:4}, at: hci_disconn_complete_evt+0x3c8/0x830 net/bluetooth/hci_event.c:3433
 #4: ffff0000de46e338 (&conn->lock#2){+.+.}-{4:4}, at: l2cap_conn_del+0x74/0x5f0 net/bluetooth/l2cap_core.c:1762
 #5: ffff80008f76b5a0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire+0x10/0x4c include/linux/rcupdate.h:330

stack backtrace:
CPU: 1 UID: 0 PID: 53 Comm: kworker/u9:0 Not tainted syzkaller #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/30/2025
Workqueue: hci4 hci_rx_work
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+0x324/0x32c kernel/locking/lockdep.c:2043
 check_noncircular+0x154/0x174 kernel/locking/lockdep.c:2175
 check_prev_add kernel/locking/lockdep.c:3165 [inline]
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x1774/0x30a4 kernel/locking/lockdep.c:5237
 lock_acquire+0x14c/0x2e0 kernel/locking/lockdep.c:5868
 touch_work_lockdep_map+0x98/0x118 kernel/workqueue.c:3951
 start_flush_work kernel/workqueue.c:4205 [inline]
 __flush_work+0x4fc/0x8c0 kernel/workqueue.c:4237
 __cancel_work_sync kernel/workqueue.c:4393 [inline]
 cancel_delayed_work_sync+0xc4/0x120 kernel/workqueue.c:4467
 l2cap_conn_del+0x460/0x5f0 net/bluetooth/l2cap_core.c:1796
 l2cap_disconn_cfm+0x90/0xe0 net/bluetooth/l2cap_core.c:7325
 hci_disconn_cfm include/net/bluetooth/hci_core.h:2121 [inline]
 hci_disconn_complete_evt+0x424/0x830 net/bluetooth/hci_event.c:3433
 hci_event_func net/bluetooth/hci_event.c:7559 [inline]
 hci_event_packet+0x704/0xf04 net/bluetooth/hci_event.c:7613
 hci_rx_work+0x320/0xb18 net/bluetooth/hci_core.c:4099
 process_one_work+0x7e8/0x155c kernel/workqueue.c:3263
 process_scheduled_works kernel/workqueue.c:3346 [inline]
 worker_thread+0x958/0xed8 kernel/workqueue.c:3427
 kthread+0x5fc/0x75c kernel/kthread.c:463
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844