When you're running under the debugger, are you starting dnsmasq with
the -d flag? If so, then I'd expect it to stop serving any other
requests whilst it's blocked doing TCP stuff. Normally, dnsmasq spawns a
new process for each TCP connection, but that is suppressed by the -d
flag, to make debugging easier.

Dnsmasq will always use TCP connections to upstream servers to get
answers to queries it receives over TCP, Have you tried the query direct
to your upstream server over TCP, to see how it copes (dig +vc command)?

Cheers,

Simon.


On 08/04/18 14:21, Dominik wrote:
> Dear dnsmasq enthusiasts,
> 
> we encountered a rather strange issue with dnsmasq, the new Cloudflare
> DNS over HTTPS service
> (https://bendews.com/posts/implement-dns-over-https/) and Netflix (only
> in this combination).
> 
> Once Netflix is started, it queries ichnaea.netflix.com. This query gets
> answered by dnsmasq, but dnsmasq becomes altogether unresponsive
> thereafter. These are the last lines logged (extra logging enabled):
> 
> Apr  8 13:30:49 dnsmasq[16025]: 3 192.168.0.6/53524 query[A]
> api-global.netflix.com from 192.168.0.6
> Apr  8 13:30:49 dnsmasq[16025]: 3 192.168.0.6/53524 forwarded
> api-global.netflix.com to 127.0.0.1
> Apr  8 13:30:49 dnsmasq[16025]: 3 192.168.0.6/53524 reply
> api-global.netflix.com is <CNAME>
> Apr  8 13:30:49 dnsmasq[16025]: 3 192.168.0.6/53524 reply
> api-global.geo.netflix.com is <CNAME>
> Apr  8 13:30:49 dnsmasq[16025]: 3 192.168.0.6/53524 reply
> api-global.latency.prodaa.netflix.com is 52.5.237.4
> Apr  8 13:30:49 dnsmasq[16025]: 3 192.168.0.6/53524 reply
> api-global.latency.prodaa.netflix.com is 52.44.197.215
> Apr  8 13:30:49 dnsmasq[16025]: 3 192.168.0.6/53524 reply
> api-global.latency.prodaa.netflix.com is 52.45.38.64
> Apr  8 13:30:49 dnsmasq[16025]: 3 192.168.0.6/53524 reply
> api-global.latency.prodaa.netflix.com is 52.45.118.37
> Apr  8 13:30:49 dnsmasq[16025]: 3 192.168.0.6/53524 reply
> api-global.latency.prodaa.netflix.com is 52.54.15.52
> Apr  8 13:30:49 dnsmasq[16025]: 3 192.168.0.6/53524 reply
> api-global.latency.prodaa.netflix.com is 52.54.22.121
> Apr  8 13:30:49 dnsmasq[16025]: 3 192.168.0.6/53524 reply
> api-global.latency.prodaa.netflix.com is 52.54.174.212
> Apr  8 13:30:49 dnsmasq[16025]: 3 192.168.0.6/53524 reply
> api-global.latency.prodaa.netflix.com is 52.54.242.21
> Apr  8 13:30:49 dnsmasq[16025]: 4 192.168.0.6/50363 query[A]
> api-global.netflix.com from 192.168.0.6
> Apr  8 13:30:49 dnsmasq[16025]: 4 192.168.0.6/50363 cached
> api-global.netflix.com is <CNAME>
> Apr  8 13:30:49 dnsmasq[16025]: 4 192.168.0.6/50363 cached
> api-global.geo.netflix.com is <CNAME>
> Apr  8 13:30:49 dnsmasq[16025]: 4 192.168.0.6/50363 cached
> api-global.latency.prodaa.netflix.com is 52.54.242.21
> Apr  8 13:30:49 dnsmasq[16025]: 4 192.168.0.6/50363 cached
> api-global.latency.prodaa.netflix.com is 52.54.174.212
> Apr  8 13:30:49 dnsmasq[16025]: 4 192.168.0.6/50363 cached
> api-global.latency.prodaa.netflix.com is 52.54.22.121
> Apr  8 13:30:49 dnsmasq[16025]: 4 192.168.0.6/50363 cached
> api-global.latency.prodaa.netflix.com is 52.54.15.52
> Apr  8 13:30:49 dnsmasq[16025]: 4 192.168.0.6/50363 cached
> api-global.latency.prodaa.netflix.com is 52.45.118.37
> Apr  8 13:30:49 dnsmasq[16025]: 4 192.168.0.6/50363 cached
> api-global.latency.prodaa.netflix.com is 52.45.38.64
> Apr  8 13:30:49 dnsmasq[16025]: 4 192.168.0.6/50363 cached
> api-global.latency.prodaa.netflix.com is 52.44.197.215
> Apr  8 13:30:49 dnsmasq[16025]: 4 192.168.0.6/50363 cached
> api-global.latency.prodaa.netflix.com is 52.5.237.4
> 
> For seeing where it hangs, we compiled dnsmasq 2.79 from source and
> added debug symbols (-g3). The crash is the same. When I interrupt
> dnsmasq while it is stalled, I see this backtrace:
> 
> #0  0x00007ffff7b15700 in __read_nocancel () at
> ../sysdeps/unix/syscall-template.S:84
> #1  0x0000555555566533 in read_write (fd=fd@entry=13,
> packet=packet@entry=0x7fffffffe334 "\002[\001", size=size@entry=1,
> rw=rw@entry=1) at util.c:654
> #2  0x000055555557029c in tcp_request (confd=13, now=1523191598,
> local_addr=0x7fffffffe410, netmask=..., auth_dns=0) at forward.c:1713
> #3  0x0000555555575999 in check_dns_listeners (now=1523191598) at
> dnsmasq.c:1745
> #4  0x000055555555d019 in main (argc=<optimized out>, argv=<optimized
> out>) at dnsmasq.c:1061
> 
> Please tell me if you would like to see any further information for
> debugging.
> 
> Best regards,
> Dominik
> 
> 
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> 

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