======================================================
WARNING: possible circular locking dependency detected
6.16.0-rc5-syzkaller-00159-g47c84997c686 #0 Not tainted
------------------------------------------------------
syz.1.7/5910 is trying to acquire lock:
ffff888025701840 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: __flush_work+0xd2/0xbc0

but task is already holding lock:
ffff888025701b38 (&conn->lock#2){+.+.}-{4:4}, at: l2cap_conn_del+0x70/0x680

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&conn->lock#2){+.+.}-{4:4}:
       lock_acquire+0x120/0x360
       __mutex_lock+0x182/0xe80
       l2cap_info_timeout+0x60/0xa0
       process_scheduled_works+0xae1/0x17b0
       worker_thread+0x8a0/0xda0
       kthread+0x711/0x8a0
       ret_from_fork+0x3fc/0x770
       ret_from_fork_asm+0x1a/0x30

-> #0 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}:
       validate_chain+0xb9b/0x2140
       __lock_acquire+0xab9/0xd20
       lock_acquire+0x120/0x360
       __flush_work+0x6b8/0xbc0
       __cancel_work_sync+0xbe/0x110
       l2cap_conn_del+0x4f0/0x680
       hci_conn_hash_flush+0x10d/0x230
       hci_dev_close_sync+0xaef/0x1330
       hci_unregister_dev+0x21a/0x510
       vhci_release+0x80/0xd0
       __fput+0x44c/0xa70
       task_work_run+0x1d4/0x260
       do_exit+0x6b5/0x22e0
       do_group_exit+0x21c/0x2d0
       get_signal+0x1286/0x1340
       arch_do_signal_or_restart+0x9a/0x750
       exit_to_user_mode_loop+0x75/0x110
       do_syscall_64+0x2bd/0x3b0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

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.1.7/5910:
 #0: ffff8881096c4dc0 (&hdev->req_lock){+.+.}-{4:4}, at: hci_unregister_dev+0x212/0x510
 #1: ffff8881096c40b8 (&hdev->lock){+.+.}-{4:4}, at: hci_dev_close_sync+0x66a/0x1330
 #2: ffffffff8f683c88 (hci_cb_list_lock){+.+.}-{4:4}, at: hci_conn_hash_flush+0xa1/0x230
 #3: ffff888025701b38 (&conn->lock#2){+.+.}-{4:4}, at: l2cap_conn_del+0x70/0x680
 #4: ffffffff8e13f160 (rcu_read_lock){....}-{1:3}, at: __flush_work+0xd2/0xbc0

stack backtrace:
CPU: 1 UID: 0 PID: 5910 Comm: syz.1.7 Not tainted 6.16.0-rc5-syzkaller-00159-g47c84997c686 #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250
 print_circular_bug+0x2ee/0x310
 check_noncircular+0x134/0x160
 validate_chain+0xb9b/0x2140
 __lock_acquire+0xab9/0xd20
 lock_acquire+0x120/0x360
 __flush_work+0x6b8/0xbc0
 __cancel_work_sync+0xbe/0x110
 l2cap_conn_del+0x4f0/0x680
 hci_conn_hash_flush+0x10d/0x230
 hci_dev_close_sync+0xaef/0x1330
 hci_unregister_dev+0x21a/0x510
 vhci_release+0x80/0xd0
 __fput+0x44c/0xa70
 task_work_run+0x1d4/0x260
 do_exit+0x6b5/0x22e0
 do_group_exit+0x21c/0x2d0
 get_signal+0x1286/0x1340
 arch_do_signal_or_restart+0x9a/0x750
 exit_to_user_mode_loop+0x75/0x110
 do_syscall_64+0x2bd/0x3b0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f9cec18e929
Code: Unable to access opcode bytes at 0x7f9cec18e8ff.
RSP: 002b:00007fff372540d8 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 000000000000e360 RCX: 00007f9cec18e929
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007f9cec3b7ba0 R08: 0000000000000001 R09: 0000001e372543cf
R10: 00007f9cec000000 R11: 0000000000000246 R12: 00007f9cec3b5fac
R13: 00007f9cec3b5fa0 R14: ffffffffffffffff R15: 00007fff372541f0
 </TASK>
