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

On Wed, Aug 9, 2017 at 6:26 PM, John Stultz [off-list ref] wrote:

On Wed, Aug 9, 2017 at 5:36 PM, Wei Wang [off-list ref] wrote:

quoted

On Wed, Aug 9, 2017 at 4:44 PM, John Stultz [off-list ref] wrote:

quoted

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

quoted

(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.

quoted

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.

So I went through another bisection around and got  9514528d92d4 ipv6:
call dst_dev_put() properly as the first bad commit again.

quoted

If you see the problem starts to happen on commit
9514528d92d4cbe086499322370155ed69f5d06c, could you try reverting all
the following commits:
(from new to old)
1eb04e7c9e63 net: reorder all the dst flags
a4c2fd7f7891 net: remove DST_NOCACHE flag
b2a9c0ed75a3 net: remove DST_NOGC flag
5b7c9a8ff828 net: remove dst gc related code
db916649b5dd ipv6: get rid of icmp6 dst garbage collector
587fea741134 ipv6: mark DST_NOGC and remove the operation of dst_free()
ad65a2f05695 ipv6: call dst_hold_safe() properly
9514528d92d4 ipv6: call dst_dev_put() properly

And reverting this set off of 4.13-rc4 seems to make the issue go away.

Is there anything I can test to help narrow down the specific problem
with that patchset?

Thanks John for confirming.
Let me spend some time on the commits and I will let you know if I
have some debug image for you to try.

Wei

thanks
-john

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