Re: [4.3] kworker busy in pm_runtime_work

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On 25.11.2015 17:42, Alan Stern wrote:
On Wed, 25 Nov 2015, Daniel J Blueman wrote:

On 23 November 2015 at 23:52, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
On Sun, 22 Nov 2015, Daniel J Blueman wrote:

On 16 November 2015 at 23:22, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> 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.

I had to use:
echo 'module xhci_hcd =p' >/sys/kernel/debug/dynamic_debug/control

and indeed we see:
[29172.246221] xhci_hcd 0000:00:14.0: get port status, actual port 11
status  = 0xe63
[29172.246222] xhci_hcd 0000:00:14.0: Get port status returned 0x507
[29172.246224] xhci_hcd 0000:00:14.0: get port status, actual port 12
status  = 0x2a0
[29172.246228] xhci_hcd 0000:00:14.0: get port status, actual port 13
status  = 0x2a0
[29172.246228] xhci_hcd 0000:00:14.0: Get port status returned 0x100
[29172.246231] xhci_hcd 0000:00:14.0: get port status, actual port 14
status  = 0x2a0
[29172.246232] xhci_hcd 0000:00:14.0: Get port status returned 0x100
[29172.246235] xhci_hcd 0000:00:14.0: Get port status returned 0x100
[29172.246248] xhci_hcd 0000:00:14.0: Get port status returned 0x100
[29172.246254] xhci_hcd 0000:00:14.0: Get port status returned 0x100
[29172.246264] xhci_hcd 0000:00:14.0: Get port status returned 0x100
[29172.246275] xhci_hcd 0000:00:14.0: Get port status returned 0x100
[29172.246285] xhci_hcd 0000:00:14.0: Get port status returned 0x507
[29172.246294] xhci_hcd 0000:00:14.0: get port status, actual port 14
status  = 0x2a0
[29172.246302] xhci_hcd 0000:00:14.0: suspend failed because a port is resuming
[29172.246321] xhci_hcd 0000:00:14.0: Get port status returned 0x107
[29172.246332] xhci_hcd 0000:00:14.0: get port status, actual port 6
status  = 0x2a0
[29172.246346] xhci_hcd 0000:00:14.0: Get port status returned 0x100
[29172.246359] xhci_hcd 0000:00:14.0: get port status, actual port 13
status  = 0x2a0
[29172.246364] xhci_hcd 0000:00:14.0: Get port status returned 0x100
[29172.246366] xhci_hcd 0000:00:14.0: get port status, actual port 15
status  = 0x2a0
[29172.246371] xhci_hcd 0000:00:14.0: suspend failed because a port is resuming
[29172.246380] xhci_hcd 0000:00:14.0: Get port status returned 0x100
[29172.246382] xhci_hcd 0000:00:14.0: get port status, actual port 1
status  = 0x2a0
[29172.246383] xhci_hcd 0000:00:14.0: Get port status returned 0x100

It's time to get some assistance from the xhci-hcd maintainer.

Mathias, Daniel's machine is spinning, trying to suspend the root hub
on the xHCI HS/FS/LS bus and failing, over and over again.  It looks
like either bus_state->resuming_ports or bus_state->port_remote_wakeup
is nonzero when it shouldn't be.

The information we have is all above.  Can you help Daniel debug this?

Alan Stern


Looks like bits in bus_state->resuming_ports may be left uncleared.

We set a bit in bus_state->resuming_ports if we get a port status event with a port
in resume link state. We only clear it when a "get port status" request finds the port
in resume state with a resume timer passed 20ms.

If something happens during this 20ms to the port, and it moves to some other link state,
then resuming_ports is never cleared.

There is a fix for what now appears to be a subset of this issue in 4.4-rc2, clearing
the bus_state->resuming_ports in case host initiated resume code moved the port link to
U0 and before the "get port status" request finds the port in resume state.
I now see that this is not enough.

I'll write a patch reordering how we check flags, timers and link state in "get port status"

Daniel, can you test a patch like this if I write it for 4.3 kernel?

-Mathias
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