netdev - Re: Asterisk deadlocks since Kernel 4.1

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Message-ID: <564D9A17.6080305@redhat.com>
Date:	Thu, 19 Nov 2015 10:44:55 +0100
From:	Florian Weimer <fweimer@...hat.com>
To:	Stefan Priebe <s.priebe@...fihost.ag>
Cc:	Thomas Gleixner <tglx@...utronix.de>, netdev@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Asterisk deadlocks since Kernel 4.1

On 11/18/2015 10:36 PM, Stefan Priebe wrote:

>> please try to get a backtrace with debugging information.  It is likely
>> that this is the make_request/__check_pf functionality in glibc, but it
>> would be nice to get some certainty.
> 
> sorry here it is. What I'm wondering is why is there ipv6 stuff? I don't
> have ipv6 except for link local.

glibc needs to know if the system has global unicast addresses if it
receives AAAA records.

It's curious that net.ipv6.conf.all.disable_ipv6=1 makes the problem go
away.  Even with that setting, the kernel seems to send two Netlink
responses.  So either this is enough to narrow the window for the race
so that no longer triggers, or there is a genuine kernel issue with
supplying the requested IPv6 Netlink response.

> Could it be this one?
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=505105#c79

No, that's on the DNS/UDP side, not in the Netlink code.

Florian
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