On Fri, Jul 14, 2023 at 03:06:12PM -0500, Dustin Marquess via dnsdist wrote:
> So far we've had instances with dnsdist 1.8.0 having a thread in a tight
> loop. OS versions seem to vary widely, so I don't believe it's a glibc bug.
>
> Config on both is the same plain config:
>
> setLocal("127.0.0.1:53", {reusePort=true})
> addLocal("127.0.0.1:53", {reusePort=true})
> addLocal("127.0.0.1:53", {reusePort=true})
> addLocal("127.0.0.1:53", {reusePort=true})
> addACL('10.0.0.0/8')
> newServer({address="10.112.104.116", checkType="A", checkClass=DNSClass.IN,
> checkName="hc.xxx.local", mustResolve=true, checkInterval=30})
> newServer({address="10.112.106.177", checkType="A", checkClass=DNSClass.IN,
> checkName="hc.xxx.local", mustResolve=true, checkInterval=30})
> newServer({address="10.9.41.68", checkType="A", checkClass=DNSClass.IN,
> checkName="hc.xxx.local", mustResolve=true, checkInterval=30})
> setServerPolicy(firstAvailable)
>
> -- Tuning
> setRingBuffersSize(1000000, 100)
> setMaxTCPClientThreads(20)
>
> -- Caching
> -- We should make these tunables configurable
> pc = newPacketCache(100000, {maxTTL=86400, minTTL=0, temporaryFailureTTL=60,
> staleTTL=60, dontAge=false})
> getPool(""):setCache(pc)
>
> -- Don't try and hit the internet
> setSecurityPollSuffix("")
>
> [pid 2990] recvfrom(-1, 0x7f3d9c0008c0, 4368, 0, NULL, NULL) = -1 EBADF (Bad
> file descriptor)
> [pid 2990] recvfrom(-1, 0x7f3d9c0008c0, 4368, 0, NULL, NULL) = -1 EBADF (Bad
> file descriptor)
> [pid 2990] recvfrom(-1, 0x7f3d9c0008c0, 4368, 0, NULL, NULL) = -1 EBADF (Bad
> file descriptor)
> [pid 2990] recvfrom(-1, 0x7f3d9c0008c0, 4368, 0, NULL, NULL) = -1 EBADF (Bad
> file descriptor)
>
> In each case, a strace shows a bad recvfrom() call in a tight loop:
>
> Obviously -1 is a bad fd! Restarting dnsdist seems to resolve it. The only
> idea I can come up with is that when dnsdist first starts, it's unable to
> contact the upstream DNS servers and that somehow causes the issue. When we
> restart it, it IS able to contact them, and so works fine.
>
> Any ideas?
>
> Thanks!
> -Dustin
This is likely https://github.com/PowerDNS/pdns/pull/12726
ATM this is not marked for backporting to 1.8.x. Don't know if that is
an omission.
-Otto
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