I just found that python consider linux implementation of getaddrinfo thread safe :

./python2.6-2.6.8/Modules/socketmodule.c:180

/* On systems on which getaddrinfo() is believed to not be thread-safe,                                                                                                                                                             
   (this includes the getaddrinfo emulation) protect access with a lock. */
#if defined(WITH_THREAD) && (defined(__APPLE__) || \
    (defined(__FreeBSD__) && __FreeBSD_version+0 < 503000) || \
    defined(__OpenBSD__) || defined(__NetBSD__) || \
    defined(__VMS) || !defined(HAVE_GETADDRINFO))
#define USE_GETADDRINFO_LOCK
#endif

Badly, it's wrong on my version of linux, and maybe others : https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=722075

So for me, looping in three threads on getaddrinfo leads me to a rapid deadlock, while reading on a NETLINK socket, after another thread wrote a DNS query on it and trying to get a response on it.

It may only be reproductible when your getaddrinfo use a NETLINK to get informations about your interfaces before doing the DNS query.