linux-kernel - Re: [syzbot] [bluetooth?] INFO: task hung in hci_conn

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Message-Id: <20240129104753.1328-1-hdanton@sina.com>
Date: Mon, 29 Jan 2024 18:47:53 +0800
From: Hillf Danton <hdanton@...a.com>
To: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc: syzbot <syzbot+a984066a63e9c1e62662@...kaller.appspotmail.com>,
	eadavis@...com,
	Peter Zijlstra <peterz@...radead.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [bluetooth?] INFO: task hung in hci_conn_failed

On Mon, 29 Jan 2024 14:53:20 +0900 Tetsuo Handa wrote:
> On 2024/01/29 13:48, Hillf Danton wrote:
> >> 3 locks held by kworker/1:2/779:
> >>  #0: ffff8880b993ccd8 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x29/0x130 kernel/sched/core.c:559
> >>  #1: ffffc900038c7d80 ((work_completion)(&aux->work)#2){+.+.}-{0:0}, at: process_one_work+0x7eb/0x15d0 kernel/workqueue.c:2609
> >>  #2: ffff888052984c80 (&aux->poke_mutex){+.+.}-{3:3}, at: __fd_array_map_delete_elem+0x125/0x2f0 kernel/bpf/arraymap.c:884
> > 
> > Could locking people shed any light on the failure of detecting the
> > poke_mutex with rq lock held?
> > 
> 
> Showing held locks (lockdep_print_held_locks()) is not a snapshot.
> Synchronous printk() can make #0 already released by the moment #2 is taken.
> 
> Please consult printk() people for possibility of making printk() from
> lockdep reports (and/or hung task reports) asynchronous.

If printk did its work well then we have difficulty explaining why RCU
stalled more than two minutes.

6 locks held by kworker/u5:0/51:
 #0: ffff88802a730d38 ((wq_completion)hci2){+.+.}-{0:0}, at: process_one_work+0x789/0x15d0 kernel/workqueue.c:2608
 #1: ffffc90000bc7d80 ((work_completion)(&hdev->cmd_sync_work)){+.+.}-{0:0}, at: process_one_work+0x7eb/0x15d0 kernel/workqueue.c:2609
 #2: ffff888020989060 (&hdev->req_lock){+.+.}-{3:3}, at: hci_cmd_sync_work+0x170/0x410 net/bluetooth/hci_sync.c:305
 #3: ffff888020988078 (&hdev->lock){+.+.}-{3:3}, at: hci_abort_conn_sync+0x150/0xb70 net/bluetooth/hci_sync.c:5337
 #4: ffffffff8ef23348 (hci_cb_list_lock){+.+.}-{3:3}, at: hci_connect_cfm include/net/bluetooth/hci_core.h:1983 [inline]
 #4: ffffffff8ef23348 (hci_cb_list_lock){+.+.}-{3:3}, at: hci_conn_failed+0x158/0x370 net/bluetooth/hci_conn.c:1289
 #5: ffffffff8d1b83f8 (rcu_state.exp_mutex){+.+.}-{3:3}, at: exp_funnel_lock kernel/rcu/tree_exp.h:324 [inline]
 #5: ffffffff8d1b83f8 (rcu_state.exp_mutex){+.+.}-{3:3}, at: synchronize_rcu_expedited+0x3ff/0x800 kernel/rcu/tree_exp.h:995