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

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Message-ID: <24c3555b-577e-4d0e-8540-7b1f009cb7d3@rowland.harvard.edu>
Date: Mon, 7 Oct 2024 12:35:44 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Oliver Neukum <oneukum@...e.com>
Cc: syzbot <syzbot+a194ded97ce38690073f@...kaller.appspotmail.com>,
	Marcello Sylvester Bauer <sylv@...v.io>, gregkh@...uxfoundation.org,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [usb?] INFO: task hung in usb_register_dev (2)

On Mon, Oct 07, 2024 at 04:16:27PM +0200, Oliver Neukum wrote:
> 
> 
> On 07.10.24 13:05, syzbot wrote:
> 
> > INFO: task kworker/1:0:25 blocked for more than 144 seconds.
> >        Not tainted 6.12.0-rc1-next-20241003-syzkaller #0
> > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> > task:kworker/1:0     state:D stack:20416 pid:25    tgid:25    ppid:2      flags:0x00004000
> > Workqueue: pm pm_runtime_work
> > Call Trace:
> >   <TASK>
> >   context_switch kernel/sched/core.c:5315 [inline]
> >   __schedule+0x1895/0x4b30 kernel/sched/core.c:6675
> >   __schedule_loop kernel/sched/core.c:6752 [inline]
> >   schedule+0x14b/0x320 kernel/sched/core.c:6767
> >   usb_poison_urb+0x1bc/0x2e0 drivers/usb/core/urb.c:763
> 
> This points to a bug in the HCD.
> usb_poison_urb() is guaranteed to make progress.
> 
> >   poison_urbs drivers/usb/class/cdc-wdm.c:342 [inline]
> >   wdm_suspend+0x174/0x380 drivers/usb/class/cdc-wdm.c:1271
> >   usb_suspend_interface drivers/usb/core/driver.c:1328 [inline]
> >   usb_suspend_both+0x2a5/0x1140 drivers/usb/core/driver.c:1433
> >   usb_runtime_suspend+0x59/0x100 drivers/usb/core/driver.c:1968
> 
> What HC is used for these tests?

Although the test's console log doesn't say, the test apparently used 
the raw gadget driver, which generally is run with dummy-hcd.  That 
driver has been having unexplained problems ever since commit 
a7f3813e589f ("usb: gadget: dummy_hcd: Switch to hrtimer transfer 
scheduler"), although I don't know if they are related to this issue.

You could try asking syzbot to run the test with a patch reverting that 
commit.

Alan Stern