[Dnsmasq-discuss] dnsmasq 2.55 failures

[Simon Kelley]

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There's no obvious fix on the CHANGELOG for this. There was something
nagging me, which was triggered by reaching the limit on DHCP leases,
but that was a crash, fixed in 2.66, and noted as having been
introduced in 2.61, so I think that's a red herring.

If this is the same bug as Dave is seeing, which seems possible it's
been around for a long time, and must therefore be very difficult to
trigger, as it's been seen rarely. The most valuable thing would
therefore be to a way to trigger it at will. The next most valuable
thing would be any information about exactly what dnsmasq is doing
whilst it's in a tight loop. An strace would be a start. (I think Dave
did that, and found no system calls being made. The same result from
you would at least give us a hint that it's all the same bug.

In any case, I'd encourage you to upgrade. There's little point
putting lots of effort into such old code.

Cheers,

Simon.



On 23/03/15 22:31, John Knight wrote:
> Hi,
> 
> We use dnsmasq 2.55 in our Linksys routers.  We have generally had 
> few problems with dnsmasq, but recently one of our customers
> reported a failure that did not recover.
> 
> On the customer's router, the maximum number of dhcp clients is
> 50. The customer happens to be a hotel and experienced a high usage
> rate and exceeded the 50 dhcp client limit.  As expected, the 50
> active clients received their IP address and those over 50 did
> not. However, the customer noticed that dns stopped working when
> this happened.  The CPU usage went to 50% (49.4% was logged to
> dnsmasq by top).  This may be 100% of single CPU as this is a dual
> CPU router. The environment is a mixed environment of both IPv4 and
> IPv6... I believe we only use dnsmasq for IPv6 for the dns
> capability; ipv4 uses dhcp and dns capability from dnsmasq.  The
> customer goes on to say that dhcp renewals were not being handled
> as well.  Customer has also added that sometimes they see issue
> with only 30 active dhcp users or so.  Apparently it requires a
> good number of users before it happens... and it does not occur
> immediately.... Sometimes a few days or more before it happens.
> 
> I looked through some of your release notes and noticed some 
> similarities on some bug reports, but did not see an exact match. 
> Does any of this make sense to you?  We tried reproducing this in
> our lab and were unsuccessful simulating the scenario.  We realize
> that our dnsmasq version is pretty old and a lot of fixes may have
> been applied since version 2.55.  If there is a good chance that
> the issues seen have been fixed in a later release, we will
> consider upgrading to a newer version.  If you could comment on the
> likelihood of a fix already being made, I would appreciate it.
> Since we cannot reproduce the problem, we will likely have to apply
> a newer version (hopefully very stable) and have customer try it...
> something we would prefer to avoid unless we have some confidence
> that the problem may already be fixed in the newer release.
> 
> Thank you for your time.  I look forward to hearing from you.
> 
> Best Regards and thanks,
> 
> John Knight
> 
> JOHN KNIGHT Senior Software Engineer
> 
> Belkin International
> 
> O +1 949 238 4543 M +1 949 351 1020 [Belkin-WeMo-Linksys]
> 
> 
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