syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.17/6697 is trying to acquire lock:
ffff0000d463f040 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: touch_work_lockdep_map+0x70/0x118 kernel/workqueue.c:3920

but task is already holding lock:
ffff0000d463f338 (&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:3236
       process_scheduled_works kernel/workqueue.c:3319 [inline]
       worker_thread+0x958/0xed8 kernel/workqueue.c:3400
       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:3922
       start_flush_work kernel/workqueue.c:4176 [inline]
       __flush_work+0x4fc/0x8c0 kernel/workqueue.c:4208
       __cancel_work_sync kernel/workqueue.c:4364 [inline]
       cancel_delayed_work_sync+0xc4/0x120 kernel/workqueue.c:4438
       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:2097 [inline]
       hci_conn_hash_flush+0x108/0x218 net/bluetooth/hci_conn.c:2599
       hci_dev_close_sync+0x89c/0x1154 net/bluetooth/hci_sync.c:5294
       hci_dev_do_close net/bluetooth/hci_core.c:501 [inline]
       hci_unregister_dev+0x204/0x4c0 net/bluetooth/hci_core.c:2715
       vhci_release+0x12c/0x17c drivers/bluetooth/hci_vhci.c:690
       __fput+0x340/0x75c fs/file_table.c:468
       ____fput+0x20/0x58 fs/file_table.c:496
       task_work_run+0x1dc/0x260 kernel/task_work.c:227
       exit_task_work include/linux/task_work.h:40 [inline]
       do_exit+0x524/0x1a14 kernel/exit.c:961
       do_group_exit+0x194/0x22c kernel/exit.c:1102
       get_signal+0x11dc/0x12f8 kernel/signal.c:3034
       arch_do_signal_or_restart+0x274/0x4434 arch/arm64/kernel/signal.c:1619
       exit_to_user_mode_loop+0x7c/0x168 kernel/entry/common.c:40
       exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
       arm64_exit_to_user_mode arch/arm64/kernel/entry-common.c:103 [inline]
       el0_svc+0x170/0x254 arch/arm64/kernel/entry-common.c:745
       el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:763
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

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 ***

5 locks held by syz.0.17/6697:
 #0: ffff0000d4cd0dc0 (&hdev->req_lock){+.+.}-{4:4}, at: hci_dev_do_close net/bluetooth/hci_core.c:499 [inline]
 #0: ffff0000d4cd0dc0 (&hdev->req_lock){+.+.}-{4:4}, at: hci_unregister_dev+0x1fc/0x4c0 net/bluetooth/hci_core.c:2715
 #1: ffff0000d4cd00b8 (&hdev->lock){+.+.}-{4:4}, at: hci_dev_close_sync+0x4c4/0x1154 net/bluetooth/hci_sync.c:5282
 #2: ffff800092bf0da8 (hci_cb_list_lock){+.+.}-{4:4}, at: hci_disconn_cfm include/net/bluetooth/hci_core.h:2094 [inline]
 #2: ffff800092bf0da8 (hci_cb_list_lock){+.+.}-{4:4}, at: hci_conn_hash_flush+0xb0/0x218 net/bluetooth/hci_conn.c:2599
 #3: ffff0000d463f338 (&conn->lock#2){+.+.}-{4:4}, at: l2cap_conn_del+0x74/0x5f0 net/bluetooth/l2cap_core.c:1762
 #4: ffff80008f9d9620 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire+0x10/0x4c include/linux/rcupdate.h:330

stack backtrace:
CPU: 1 UID: 0 PID: 6697 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/30/2025
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:3922
 start_flush_work kernel/workqueue.c:4176 [inline]
 __flush_work+0x4fc/0x8c0 kernel/workqueue.c:4208
 __cancel_work_sync kernel/workqueue.c:4364 [inline]
 cancel_delayed_work_sync+0xc4/0x120 kernel/workqueue.c:4438
 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:2097 [inline]
 hci_conn_hash_flush+0x108/0x218 net/bluetooth/hci_conn.c:2599
 hci_dev_close_sync+0x89c/0x1154 net/bluetooth/hci_sync.c:5294
 hci_dev_do_close net/bluetooth/hci_core.c:501 [inline]
 hci_unregister_dev+0x204/0x4c0 net/bluetooth/hci_core.c:2715
 vhci_release+0x12c/0x17c drivers/bluetooth/hci_vhci.c:690
 __fput+0x340/0x75c fs/file_table.c:468
 ____fput+0x20/0x58 fs/file_table.c:496
 task_work_run+0x1dc/0x260 kernel/task_work.c:227
 exit_task_work include/linux/task_work.h:40 [inline]
 do_exit+0x524/0x1a14 kernel/exit.c:961
 do_group_exit+0x194/0x22c kernel/exit.c:1102
 get_signal+0x11dc/0x12f8 kernel/signal.c:3034
 arch_do_signal_or_restart+0x274/0x4434 arch/arm64/kernel/signal.c:1619
 exit_to_user_mode_loop+0x7c/0x168 kernel/entry/common.c:40
 exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
 arm64_exit_to_user_mode arch/arm64/kernel/entry-common.c:103 [inline]
 el0_svc+0x170/0x254 arch/arm64/kernel/entry-common.c:745
 el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:763
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596