[dnsdist] dnsdist 1.8.0 thread spinning

[Dustin Marquess]

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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.powerdns.com/pipermail/dnsdist/attachments/20230714/416a469d/attachment.htm>