Re: [syzbot] [bluetooth?] INFO: task hung in hci_conn_failed

[Hillf Danton <hdanton@sina.com>]

On Tue, 30 Jan 2024 07:45:06 -0800
> 6 locks held by kworker/u5:5/5431:
>  #0: ffff888027f29538 ((wq_completion)hci5){+.+.}-{0:0}, at: process_one_work+0x789/0x15d0 kernel/workqueue.c:2608
>  #1: ffffc90009bffd80 ((work_completion)(&hdev->cmd_sync_work)){+.+.}-{0:0}, at: process_one_work+0x7eb/0x15d0 kernel/workqueue.c:2609
>  #2: ffff888079359060 (&hdev->req_lock){+.+.}-{3:3}, at: hci_cmd_sync_work+0x170/0x410 net/bluetooth/hci_sync.c:305
>  #3: ffff888079358078 (&hdev->lock){+.+.}-{3:3}, at: hci_abort_conn_sync+0x150/0xb50 net/bluetooth/hci_sync.c:5337
>  #4: ffffffff8ef238c8 (hci_cb_list_lock){+.+.}-{3:3}, at: hci_connect_cfm include/net/bluetooth/hci_core.h:1983 [inline]
>  #4: ffffffff8ef238c8 (hci_cb_list_lock){+.+.}-{3:3}, at: hci_conn_failed+0x158/0x370 net/bluetooth/hci_conn.c:1289
>  #5: ffffffff8d1b8438 (rcu_state.exp_mutex){+.+.}-{3:3}, at: exp_funnel_lock kernel/rcu/tree_exp.h:324 [inline]
>  #5: ffffffff8d1b8438 (rcu_state.exp_mutex){+.+.}-{3:3}, at: synchronize_rcu_expedited+0x3ff/0x800 kernel/rcu/tree_exp.h:995
> 3 locks held by kworker/1:5/5500:
> 3 locks held by kworker/0:8/5556:
> 3 locks held by kworker/1:6/5586:
> 3 locks held by kworker/1:7/5659:
> 2 locks held by dhcpcd/20271:
>  #0: ffff88808e304130 (sk_lock-AF_PACKET){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1691 [inline]
>  #0: ffff88808e304130 (sk_lock-AF_PACKET){+.+.}-{0:0}, at: packet_do_bind+0x2c/0xf50 net/packet/af_packet.c:3202
>  #1: ffffffff8d1b8438 (rcu_state.exp_mutex){+.+.}-{3:3}, at: exp_funnel_lock kernel/rcu/tree_exp.h:324 [inline]
>  #1: ffffffff8d1b8438 (rcu_state.exp_mutex){+.+.}-{3:3}, at: synchronize_rcu_expedited+0x3ff/0x800 kernel/rcu/tree_exp.h:995

With Boqun's patch, the failure of detecting mutex with runqueue lock
held disappeared but RCU stalled more than two minutes as before.