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

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Message-ID: <0abd3cbd-0e8a-43b2-8cb0-6556297aa7c9@suse.com>
Date: Mon, 21 Oct 2024 10:04:52 +0200
From: Oliver Neukum <oneukum@...e.com>
To: syzbot <syzbot+f342ea16c9d06d80b585@...kaller.appspotmail.com>,
 gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
 linux-usb@...r.kernel.org, stern@...land.harvard.edu, sylv@...v.io,
 syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [usb?] INFO: task hung in usb_port_suspend

On 20.10.24 18:38, syzbot wrote:
  
> INFO: task kworker/0:0:8 blocked for more than 143 seconds.
>        Not tainted 6.12.0-rc3-syzkaller-00051-g07b887f8236e #0
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> task:kworker/0:0     state:D stack:24544 pid:8     tgid:8     ppid:2      flags:0x00004000
> Workqueue: pm pm_runtime_work
> Call Trace:
>   <TASK>
>   context_switch kernel/sched/core.c:5322 [inline]
>   __schedule+0x105f/0x34b0 kernel/sched/core.c:6682
>   __schedule_loop kernel/sched/core.c:6759 [inline]
>   schedule+0xe7/0x350 kernel/sched/core.c:6774

And this sleeps forever. This must not happen.
>   usb_kill_urb.part.0+0x1ca/0x250 drivers/usb/core/urb.c:713
>   usb_kill_urb+0x83/0xa0 drivers/usb/core/urb.c:702

We are changing our mind, presumably due to a timeout
>   usb_start_wait_urb+0x255/0x4c0 drivers/usb/core/message.c:65

We are sending a control message, presumably to enable
remote wakeup
>   usb_internal_control_msg drivers/usb/core/message.c:103 [inline]
>   usb_control_msg+0x327/0x4b0 drivers/usb/core/message.c:154
>   usb_enable_remote_wakeup drivers/usb/core/hub.c:3365 [inline]
>   usb_port_suspend+0x339/0xf10 drivers/usb/core/hub.c:3472

Suspending ...
>   usb_generic_driver_suspend+0xeb/0x1d0 drivers/usb/core/generic.c:302
>   usb_suspend_device drivers/usb/core/driver.c:1272 [inline]
>   usb_suspend_both+0x66d/0x9c0 drivers/usb/core/driver.c:1443
>   usb_runtime_suspend+0x49/0x180 drivers/usb/core/driver.c:1968

This very much looks like the HC driver used to run these tests
can hand in unlink. If that happens there is nothing usbcore
or a driver can do.
As this is now reproducible I would suggest a bisection. Brute force,
but I see no good alternative.

Syzbot is an important tool and if the HC driver it uses is unreliable,
the whole thing becomes unreliable and that is most undesirable.

	Regards
		Oliver