Re: [PATCH] Tests for res_init

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Sat, Jun 3, 2017 at 10:39 PM, Florian Weimer <fweimer@redhat.com> wrote:
> On 06/04/2017 07:10 AM, H.J. Lu wrote:
>
>> This commit:
>>
>> commit c0303efeab7391ec51c337e0ac5740860ad01fe7
>> Author: Jesper Dangaard Brouer <brouer@redhat.com>
>> Date:   Mon Jan 9 16:04:09 2017 +0100
>>
>>     net: reduce cycles spend on ICMP replies that gets rate limited
>>
>>     This patch split the global and per (inet)peer ICMP-reply limiter
>>     code, and moves the global limit check to earlier in the packet
>>     processing path.  Thus, avoid spending cycles on ICMP replies that
>>     gets limited/suppressed anyhow.
>>
>>     The global ICMP rate limiter icmp_global_allow() is a good solution,
>>     it just happens too late in the process.  The kernel goes through the
>>     full route lookup (return path) for the ICMP message, before taking
>>     the rate limit decision of not sending the ICMP reply.
>>
>>     Details: The kernels global rate limiter for ICMP messages got added
>>     in commit 4cdf507d5452 ("icmp: add a global rate limitation").  It is
>>     a token bucket limiter with a global lock.  It brilliantly avoids
>>     locking congestion by only updating when 20ms (HZ/50) were elapsed. It
>>     can then avoids taking lock when credit is exhausted (when under
>>     pressure) and time constraint for refill is not yet meet.
>>
>>     Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
>>     Acked-by: Eric Dumazet <edumazet@google.com>
>>     Signed-off-by: David S. Miller <davem@davemloft.net>
>>
>> is the culprit.   This patch for kernel 4.11.3 reverts it and fixes
>> my problems.
>
> Makes sense.  There does not seem to be any check left that localhost
> responses aren't rate-limited.  Furthermore, the rate limit is not
> namespace-specific, so the network namespace used in the test doesn't
> provide any isolation.
>
> I think I'll have enough information to write a reduced test case, and
> I'll approach the kernel developers to get this fixed upstream.
>

I opened a Fedora 25 bug:

https://bugzilla.redhat.com/show_bug.cgi?id=1458586

Hopefully, I will be notified when it is fixed in Fedora 25.

-- 
H.J.