linux-kernel - Re: [syzbot] [usb?] INFO: task hung in hub

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Message-ID: <fc5f7057-1c91-4354-89d5-f8bdeeae988a@rowland.harvard.edu>
Date: Wed, 2 Jul 2025 10:34:51 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Hillf Danton <hdanton@...a.com>
Cc: syzbot <syzbot+d630bd89141124cc543e@...kaller.appspotmail.com>,
	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Boqun Feng <boqun.feng@...il.com>, linux-usb@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [usb?] INFO: task hung in hub_activate (3)

On Wed, Jul 02, 2025 at 04:05:14PM +0800, Hillf Danton wrote:
> On Tue, 01 Jul 2025 17:50:28 -0700
> > Hello,
> > 
> > syzbot found the following issue on:
> > 
> > HEAD commit:    1343433ed389 Add linux-next specific files for 20250630
> > git tree:       linux-next
> > console output: https://syzkaller.appspot.com/x/log.txt?x=10d1f88c580000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=66357ac5b0466f16
> > dashboard link: https://syzkaller.appspot.com/bug?extid=d630bd89141124cc543e
> > compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
> > 
> > Unfortunately, I don't have any reproducer for this issue yet.
> > 
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/b005e1db0f8c/disk-1343433e.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/cb3aa8bfd514/vmlinux-1343433e.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/e01227599a09/bzImage-1343433e.xz
> > 
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+d630bd89141124cc543e@...kaller.appspotmail.com
> > 
> > INFO: task kworker/0:0:9 blocked for more than 143 seconds.
> >       Not tainted 6.16.0-rc4-next-20250630-syzkaller #0
> > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > task:kworker/0:0     state:D stack:21240 pid:9     tgid:9     ppid:2      task_flags:0x4208060 flags:0x00004000
> > Workqueue: events_power_efficient hub_init_func2
> > Call Trace:
> >  <TASK>
> >  context_switch kernel/sched/core.c:5313 [inline]
> >  __schedule+0x16f5/0x4d00 kernel/sched/core.c:6696
> >  __schedule_loop kernel/sched/core.c:6774 [inline]
> >  schedule+0x165/0x360 kernel/sched/core.c:6789
> >  schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:6846
> >  __mutex_lock_common kernel/locking/mutex.c:679 [inline]
> >  __mutex_lock+0x724/0xe80 kernel/locking/mutex.c:747
> >  device_lock include/linux/device.h:884 [inline]
> >  hub_activate+0xb7/0x1ea0 drivers/usb/core/hub.c:1096
> >  process_one_work kernel/workqueue.c:3239 [inline]
> >  process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3322
> >  worker_thread+0x8a0/0xda0 kernel/workqueue.c:3403
> >  kthread+0x70e/0x8a0 kernel/kthread.c:463
> >  ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
> >  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
> >  </TASK>
> 
> Due to lockdep_set_novalidate_class(&dev->mutex) in device_initialize(),
> task hung instead of deadlock is reported once more.
> 
> 	kworker/0:0:9		kworker/0:5:5923
> 	---			---
> 	hub_init_func2()	usb_disconnect()
> 				device_lock()
> 	device_lock()		hub_disconnect()
> 				hub_quiesce()
> 				flush_delayed_work(&hub->init_work);
> 	*** DEADLOCK ***

This analysis looks right.  How would you fix the deadlock?  Make 
hub_disconnect do device_unlock() and device_lock() around the 
flush_delayed_work() call?

Alan Stern