Received-SPF: pass (google.com: domain of linux-kernel+bounces-42564-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45e3:2400::1 as permitted sender) client-ip=2604:1380:45e3:2400::1;
From: Hillf Danton <hdanton@sina.com>
To: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: syzbot <syzbot+a984066a63e9c1e62662@syzkaller.appspotmail.com>,
	eadavis@qq.com,
	Peter Zijlstra <peterz@infradead.org>,
	Boqun Feng <boqun.feng@gmail.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	linux-kernel@vger.kernel.org,
	syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [bluetooth?] INFO: task hung in hci_conn_failed
Date: Mon, 29 Jan 2024 18:47:53 +0800
Message-Id: <20240129104753.1328-1-hdanton@sina.com>
In-Reply-To: <4c59b146-df67-48d8-9378-3948dd6fb427@I-love.SAKURA.ne.jp>
References: <tencent_4A66EF6ACD6878526F542C2D6D109794E80A@qq.com> <20240129044824.1218-1-hdanton@sina.com>
Precedence: bulk
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit

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