netdev - Re: [RFC] net: usbnet: prevent buggy devices from killing us

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Date:	Thu, 24 Jan 2013 14:42:09 +0100
From:	Bjørn Mork <bjorn@...k.no>
To:	Oliver Neukum <oneukum@...e.de>
Cc:	linux-usb@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [RFC] net: usbnet: prevent buggy devices from killing us

Oliver Neukum <oneukum@...e.de> writes:

> On Thursday 24 January 2013 13:47:40 Bjørn Mork wrote:
>> Oliver Neukum <oneukum@...e.de> writes:
>> > On Thursday 24 January 2013 12:22:54 Bjørn Mork wrote:
>> >
>> >> Sorry for being daft, but how do I code the "20 among the last 30" part
>> >> there?
>> >
>> > Just by agreeing that you can live with false negatives but not false positives
>> >
>> > if (++counter > 30) {
>> > 	counter = bogus = 0;
>> > } else {
>> > 	if (is_bogus(packet)
>> > 		bogus++;
>> > 	if (bogus > counter/2)
>
> Should probably be something like bogus > counter/2 + 10

right

>> > 		throttle();
>> > }
>> 
>> So, add two new counters to struct usbnet for this?  That seems a little
>> overkill to me, but I don't see how else to implement anything like that.
>
> Memory is cheap.

OK

>> It is still not completely clear to me how the throttling/unthrottling
>> should be done.  It tested with static counters (to avoid having to
>> rebuild everything for this test) and a new EVENT_RX_THROTTLE flag.
>> Still on top of my previous patch just for safety while testing, as I am
>> fed up of having to reboot all the time :-)
>> 
>> Doing the flag test in rx_submit seems simpler than trying to track all
>> the places this is called.  Still checking the dev->done.qlen to be able
>> to unthrottle.
>
> Ideally we would do some error handling. Does the device keep spewing
> zero packets for all eternity?

Yes. The only way to get rid of the bug once it has triggered seems to
be powering the device off/on.  So unthrottling is not important for
this device.  But I guess it will be for other devices with more
temporary problems.



Bjørn
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