Recursive lockdep warning with 4.14-rc8 kernel

[Bastien Nocera <hadess@hadess.net>]

Hey,

During my testing trying to pair the new XBox One S Bluetooth
controller, I hit a lockdep warning.

[   56.415138] ============================================
[   56.415139] WARNING: possible recursive locking detected
[   56.415142] 4.14.0-0.rc8.git1.1.bt2.fc28.x86_64 #1 Not tainted
[   56.415143] --------------------------------------------
[   56.415145] kworker/u9:2/579 is trying to acquire lock:
[   56.415147]  (sk_lock-AF_BLUETOOTH-BTPROTO_L2CAP){+.+.}, at: [<ffffffffc08dc262>] bt_accept_enqueue+0x42/0xc0 [bluetooth]
[   56.415167] 
               but task is already holding lock:
[   56.415168]  (sk_lock-AF_BLUETOOTH-BTPROTO_L2CAP){+.+.}, at: [<ffffffffc0919e5d>] l2cap_sock_new_connection_cb+0x1d/0xa0 [bluetooth]
[   56.415184] 
               other info that might help us debug this:
[   56.415186]  Possible unsafe locking scenario:

[   56.415187]        CPU0
[   56.415188]        ----
[   56.415189]   lock(sk_lock-AF_BLUETOOTH-BTPROTO_L2CAP);
[   56.415192]   lock(sk_lock-AF_BLUETOOTH-BTPROTO_L2CAP);
[   56.415194] 
                *** DEADLOCK ***

[   56.415196]  May be due to missing lock nesting notation

[   56.415198] 5 locks held by kworker/u9:2/579:
[   56.415199]  #0:  ("%s"hdev->name#2){+.+.}, at: [<ffffffffae0d4e90>] process_one_work+0x1d0/0x6a0
[   56.415206]  #1:  ((&hdev->rx_work)){+.+.}, at: [<ffffffffae0d4e90>] process_one_work+0x1d0/0x6a0
[   56.415211]  #2:  (&conn->chan_lock){+.+.}, at: [<ffffffffc09120e3>] l2cap_connect+0x93/0x5d0 [bluetooth]
[   56.415226]  #3:  (&chan->lock/2){+.+.}, at: [<ffffffffc09120fd>] l2cap_connect+0xad/0x5d0 [bluetooth]
[   56.415239]  #4:  (sk_lock-AF_BLUETOOTH-BTPROTO_L2CAP){+.+.}, at: [<ffffffffc0919e5d>] l2cap_sock_new_connection_cb+0x1d/0xa0 [bluetooth]
[   56.415252] 
               stack backtrace:
[   56.415255] CPU: 0 PID: 579 Comm: kworker/u9:2 Not tainted 4.14.0-0.rc8.git1.1.bt2.fc28.x86_64 #1
[   56.415257] Hardware name: Dell Inc. OptiPlex 9020M/0Y5DDC, BIOS A07 09/10/2015
[   56.415267] Workqueue: hci0 hci_rx_work [bluetooth]
[   56.415269] Call Trace:
[   56.415274]  dump_stack+0x8e/0xd6
[   56.415279]  __lock_acquire+0x6af/0x1320
[   56.415288]  ? bt_accept_enqueue+0x42/0xc0 [bluetooth]
[   56.415291]  ? __lock_is_held+0x65/0xb0
[   56.415294]  ? mark_held_locks+0x5f/0x90
[   56.415299]  lock_acquire+0xa3/0x1f0
[   56.415301]  ? lock_acquire+0xa3/0x1f0
[   56.415310]  ? bt_accept_enqueue+0x42/0xc0 [bluetooth]
[   56.415314]  lock_sock_nested+0x76/0xa0
[   56.415323]  ? bt_accept_enqueue+0x42/0xc0 [bluetooth]
[   56.415332]  bt_accept_enqueue+0x42/0xc0 [bluetooth]
[   56.415343]  l2cap_sock_new_connection_cb+0x62/0xa0 [bluetooth]
[   56.415353]  l2cap_connect+0x136/0x5d0 [bluetooth]
[   56.415358]  ? sched_clock+0x9/0x10
[   56.415368]  ? l2cap_recv_frame+0x7a6/0x2900 [bluetooth]
[   56.415373]  ? __mutex_unlock_slowpath+0x50/0x2f0
[   56.415383]  l2cap_recv_frame+0x7be/0x2900 [bluetooth]
[   56.415393]  ? hci_rx_work+0x472/0x5f0 [bluetooth]
[   56.415404]  l2cap_recv_acldata+0x2ff/0x310 [bluetooth]
[   56.415413]  hci_rx_work+0x494/0x5f0 [bluetooth]
[   56.415417]  process_one_work+0x250/0x6a0
[   56.415421]  worker_thread+0x3d/0x3b0
[   56.415424]  kthread+0x133/0x150
[   56.415426]  ? process_one_work+0x6a0/0x6a0
[   56.415428]  ? kthread_create_on_node+0x70/0x70
[   56.415431]  ret_from_fork+0x2a/0x40