Re: unregister_netdevice: waiting for eth0 to become free. Usage count = 1

On Wed, Aug 9, 2017 at 4:34 PM, Cong Wang [off-list ref] wrote:

(Cc'ing Wei whose commit was blamed)

On Mon, Aug 7, 2017 at 2:15 PM, John Stultz [off-list ref] wrote:

quoted

On Mon, Aug 7, 2017 at 2:05 PM, John Stultz [off-list ref] wrote:

quoted

So, with recent testing with my HiKey board, I've been noticing some
quirky behavior with my USB eth adapter.

Basically, pluging the usb eth adapter in and then removing it, when
plugging it back in I often find that its not detected, and the system
slowly spits out the following message over and over:
  unregister_netdevice: waiting for eth0 to become free. Usage count = 1

The other bit is that after this starts printing, the board will no
longer reboot (it hangs continuing to occasionally print the above
message), and I have to manually reset the device.

So this warning is not temporarily shown but lasts until a reboot,
right? If so it is a dst refcnt leak.

Correct, once I get into the state it lasts until a reboot.

How reproducible is it for you? From my reading, it seems always
reproduced when you unplug and plug your usb eth interface?
Is there anything else involved? For example, network namespace.

So with 4.13-rc3/4 I seem to trigger it easily, often with the first
unplug of the USB eth adapter.

But as I get back closer to 4.12, it seemingly becomes harder to
trigger, but sometimes still happens.

So far, I've not been able to trigger it with 4.12.

I don't think network namespaces are involved?  Though its out of my
area, so AOSP may be using them these days.  Is there a simple way to
check?

I'll also do another bisection to see if the bad point moves back any further.

thanks
-john