linux-kernel - Re: [4.3] kworker busy in pm_runtime

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Date:	Mon, 23 Nov 2015 10:52:42 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Daniel J Blueman <daniel@...ra.org>
cc:	USB list <linux-usb@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [4.3] kworker busy in pm_runtime_work

On Sun, 22 Nov 2015, Daniel J Blueman wrote:

> On 16 November 2015 at 23:22, Alan Stern <stern@...land.harvard.edu> wrote:
> > On Mon, 16 Nov 2015, Daniel J Blueman wrote:
> >
> >> Tuning USB suspend [1] in 4.3 on a Dell XPS 15 9553 (Skylake), I see a
> >> kworker thread spinning in rpm_suspend [2].
> >>
> >> What is the most useful debug to get here beyond the immediate [3]?
> >
> > You can try doing:
> >
> >         echo 'module usbcore =p' >/sys/kernel/debug/dynamic_debug/control
> 
> kworker and ksoftirqd spinning occurs when I echo 'auto' to all the
> USB control entries. Using Alan's excellent tip, we see this being
> logged repeatedly at a high rate:
> [  353.245180] usb usb1-port4: status 0107 change 0000
> [  353.245194] usb usb1-port12: status 0507 change 0000
> [  353.245202] hub 1-0:1.0: state 7 ports 16 chg 0000 evt 0000
> [  353.245203] hub 1-0:1.0: hub_suspend
> [  353.245205] usb usb1: bus auto-suspend, wakeup 1
> [  353.245206] usb usb1: bus suspend fail, err -16
> [  353.245207] hub 1-0:1.0: hub_resume
> ...
> 
> So, EBUSY. Both the webcam is not open, and the bluetooth interface
> [1] is rfkill'd; the situation occurs even if I unload all related
> modules.
> 
> What further debug would be useful?
> 
> Thanks!
>   Daniel
> 
> -- [1]
> 
> Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
> Bus 001 Device 002: ID 0a5c:6410 Broadcom Corp.
> Bus 001 Device 003: ID 1bcf:2b95 Sunplus Innovation Technology Inc.
> Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

Since bus 1 uses an xHCI controller, you should do:

	echo 'module xhci-hcd =p' >/sys/kernel/debug/dynamic_debug/control

I'm reasonably sure this will end up printing "suspend failed 
because a port is resuming", since that's the only place where 
xhci_bus_suspend() fails with -EBUSY, but you should try it to confirm 
this.

Alan Stern

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