Add an awful secondary timeout to fix wedged requests

This is an attempt to mitigate #3842 by adding yet-another-timeout

synapse/http/matrixfederationclient.py

@@ -42,6 +42,7 @@ from synapse.api.errors import (
 )
 from synapse.http.endpoint import matrix_federation_endpoint
 from synapse.util import logcontext
+from synapse.util.async_helpers import timeout_no_seriously
 from synapse.util.logcontext import make_deferred_yieldable
 from synapse.util.metrics import Measure
 
@@ -228,6 +229,16 @@ class MatrixFederationHttpClient(object):
                     )
                     request_deferred.addTimeout(_sec_timeout, self.hs.get_reactor())
 
+                    # Sometimes the timeout above doesn't work, so lets hack yet
+                    # another layer of timeouts in in the vain hope that at some
+                    # point the world made sense and this really really really
+                    # should work.
+                    request_deferred = timeout_no_seriously(
+                        request_deferred,
+                        timeout=_sec_timeout * 2,
+                        reactor=self.hs.get_reactor(),
+                    )
+
                     with Measure(self.clock, "outbound_request"):
                         response = yield make_deferred_yieldable(
                             request_deferred,