Re: cdc_ether flooding kernel logs since bfe9b9d2d

[Kristian Evensen]

Hi,

On Wed, Nov 30, 2016 at 4:17 PM, Oliver Neukum  wrote:
> On Tue, 2016-11-29 at 14:41 +0100, Kristian Evensen wrote:
>> I don't know which of the two behaviors (if any) are "correct" or what
>> the best way to solve this problem is. One options is to remove the
>> code from the generic usbnet_cdc_status() function and move it to a
>> ZTE-specific status function inside cdc_ether.
>
> Hi,
>
> please do so. This looks like the cleanest approach.

Ok, great. I will do this right away and submit a patch tonight.

Again, sorry for this.

-Kristian
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Re: cdc_ether flooding kernel logs since bfe9b9d2d

[Oliver Neukum]

On Tue, 2016-11-29 at 14:41 +0100, Kristian Evensen wrote:
> I don't know which of the two behaviors (if any) are "correct" or what
> the best way to solve this problem is. One options is to remove the
> code from the generic usbnet_cdc_status() function and move it to a
> ZTE-specific status function inside cdc_ether.

Hi,

please do so. This looks like the cleanest approach.

Regards
Oliver


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Re: cdc_ether flooding kernel logs since bfe9b9d2d

[Kristian Evensen]

Hi,

On Tue, Nov 29, 2016 at 11:27 AM, Henning Schild
 wrote:
> commit bfe9b9d2d introduced a workaround for link status detection.
> That workaround seems to cause a tight loop of usbnet_cdc_status being
> called all the time, which in turn prints
> "kevent 11 may have been dropped" in the kernel log all the time.

Thanks for letting me/us know. I spent some time looking into the
problem now and can reproduce it with a fairly recent cdc_ether dongle
that I just got (also Linksys). The cause is that after every
(incoming?) interrupt, usbnet_cdc_status() is called. Each interrupt
contains a USB_CDC_NOTIFY_NETWORK_CONNECTION notification, reporting
that the carrier is on. After my change, this will cause the interface
to be set as down and then up for each interrupt, since the carrier is
already is already available (__LINK_STATE_NOCARRIER is not set). I
also captured the traffic on the correct USB bus and see these
interrupts happening multiple times per second.

When re-testing with the devices I used when developing the patch, I
do not see this behavior. I only see one (with devices I assumed to be
working fine) or two (MF823/910) interrupts. Other than that, it is
mostly bulk transfers.

I don't know which of the two behaviors (if any) are "correct" or what
the best way to solve this problem is. One options is to remove the
code from the generic usbnet_cdc_status() function and move it to a
ZTE-specific status function inside cdc_ether.

-Kristian
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cdc_ether flooding kernel logs since bfe9b9d2d

[Henning Schild]

Hi,

commit bfe9b9d2d introduced a workaround for link status detection.
That workaround seems to cause a tight loop of usbnet_cdc_status being
called all the time, which in turn prints
"kevent 11 may have been dropped" in the kernel log all the time.

I am not sure about the semantics, i just found the commit causing
the problem and a workaround for my device.

For me just removing the workaround block works, so does inserting a
break so usbnet_link_change does not get called twice. But with the
break ethtool wont report a link anymore. I am guessing that calling
usbnet_link_change twice in a row (off and then on) will trigger an
event that ends up on the very same codepath.

The problem is already described in several bugtrackers:
https://bugzilla.kernel.org/show_bug.cgi?id=185641
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1626371
https://bugzilla.redhat.com/show_bug.cgi?id=1383810

My device is a "13b1:0041 Linksys".

regards,
Henning
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