Re: [BUG] 4.10-rc8 - ping spinning?

[Soheil Hassas Yeganeh]

On Thu, Feb 16, 2017 at 11:08 AM,  <lkml@xxxxxxxxxxx> wrote:
> On Thu, Feb 16, 2017 at 10:52:19AM -0500, Soheil Hassas Yeganeh wrote:
>> On Thu, Feb 16, 2017 at 10:50 AM, Soheil Hassas Yeganeh
>> <soheil@xxxxxxxxxx> wrote:
>> > Thank you Vito for the report.
>> >
>> > The patch you cited actually resolves a similar backward compatibility
>> > problem for traceroute.
>> >
>> > I suspect the problem here is that there's a local error queued on the
>> > error queue after an ICMP message. ping apparently expect the
>> > sk->sk_err to be set for the local errors as well, and hence the
>> > error. Ideally, ping should read the error queue if there an EPOLLERR,
>> > because local errors never sk->sk_err on their own. That is, if we
>> > have
>>
>> [oops] That is, if we have only one local error on the error queue, we
>> cannot rely on having an error on recvmsg (i.e., sk->sk_err being set)
>> even in 4.9.
>>
>> <snip>
>
> Hi Soheil,
>
> This doesn't appear to be trivially reproducible here by just running ping
> as it were originally discovered.  I'll see if I can reliably cause the
> malfunction somehow, but until then I can't meaningfully test patches.
>
> Perhaps a form of fault injection would make more sense if there's a
> reasonable idea of what this is stemming from?

I tried to generate different ICMP errors as well as local errors, but
unfortunately haven't been able to reproduce the problem.

> I've opened an issue with iputils on github in the event that this is found
> to be a ping bug.  Your input might be helpful there as well:
> https://github.com/iputils/iputils/issues/74

Sent a pull request. Although, we might want to at least confirm the
userspace patch fixes the issue in ping.

Thanks!
Soheil

> Thanks,
> Vito Caputo