Jonathan Giddy writes:

Here's a patch to fix the race condition, which wasn't fixed by Rob's
patch.  It holds the gethostbyname lock until the results are copied out,
which means that this lock and the Python global lock are held at the same
time.  This shouldn't be a problem as long as the gethostbyname lock is
always acquired when the global lock is not held.

Modules/socketmodule.c

@@ -328,6 +328,7 @@ BUILD_FUNC_DEF_2(setipaddr, char*,name, struct sockaddr_in *,addr_ret)
 {
 	struct hostent *hp;
 	int d1, d2, d3, d4;
+	int h_length;
 	char ch;
 #ifdef HAVE_GETHOSTBYNAME_R
 	struct hostent hp_allocated;
@@ -368,9 +369,6 @@ BUILD_FUNC_DEF_2(setipaddr, char*,name, struct sockaddr_in *,addr_ret)
 	PyThread_acquire_lock(gethostbyname_lock,1);
 #endif
 	hp = gethostbyname(name);
-#if defined(WITH_THREAD) && !defined(MS_WINDOWS)
-	PyThread_release_lock(gethostbyname_lock);
-#endif
 #endif /* HAVE_GETHOSTBYNAME_R */
 	Py_END_ALLOW_THREADS
 
@@ -381,11 +379,18 @@ BUILD_FUNC_DEF_2(setipaddr, char*,name, struct sockaddr_in *,addr_ret)
 		PyErr_SetString(PySocket_Error, (char *)hstrerror(h_errno));
 #else
 		PyErr_SetString(PySocket_Error, "host not found");
+#endif
+#if defined(WITH_THREAD) && !defined(HAVE_GETHOSTBYNAME_R) && !defined(MS_WINDOWS)
+		PyThread_release_lock(gethostbyname_lock);
 #endif
 		return -1;
 	}
 	memcpy((char *) &addr_ret->sin_addr, hp->h_addr, hp->h_length);
-	return hp->h_length;
+	h_length = hp->h_length;
+#if defined(WITH_THREAD) && !defined(HAVE_GETHOSTBYNAME_R) && !defined(MS_WINDOWS)
+	PyThread_release_lock(gethostbyname_lock);
+#endif
+	return h_length;
 }
 
 
@@ -1409,6 +1414,7 @@ BUILD_FUNC_DEF_2(PySocket_gethostbyname_ex,PyObject *,self, PyObject *,args)
 	char *name;
 	struct hostent *h;
 	struct sockaddr_in addr;
+	PyObject *ret;
 #ifdef HAVE_GETHOSTBYNAME_R
 	struct hostent hp_allocated;
 	char buf[16384];
@@ -1434,12 +1440,13 @@ BUILD_FUNC_DEF_2(PySocket_gethostbyname_ex,PyObject *,self, PyObject *,args)
 	PyThread_acquire_lock(gethostbyname_lock,1);
 #endif
 	h = gethostbyname(name);
-#if defined(WITH_THREAD) && !defined(MS_WINDOWS)
-	PyThread_release_lock(gethostbyname_lock);
-#endif
 #endif /* HAVE_GETHOSTBYNAME_R */
 	Py_END_ALLOW_THREADS
-	return gethost_common(h,&addr);
+	ret = gethost_common(h,&addr);
+#if defined(WITH_THREAD) && !defined(HAVE_GETHOSTBYNAME_R) && !defined(MS_WINDOWS)
+	PyThread_release_lock(gethostbyname_lock);
+#endif
+	return ret;
 }
 
 static char ghbn_ex_doc[] =