mod_http3: fix a session allocator race, a stuck graceful drain and a blocked-stream spin

changes-entries/h3_blocked_stream_spin.txt

@@ -0,0 +1,4 @@
+  *) mod_http3: Fixed an event-thread spin while a client holds its
+     flow-control window shut: a blocked stream is now blocked again each time
+     nghttp3 offers it.
+     [Alexander Gerasimov <codeguard gmail.com>]

changes-entries/h3_drain_pending_handshakes.txt

@@ -0,0 +1,4 @@
+  *) mod_http3: Fixed a graceful restart that never ended: a handshake still
+     pending when the child started to drain did not finish or time out, so
+     the old child kept its connection count and the port.
+     [Alexander Gerasimov <codeguard gmail.com>]

changes-entries/h3_session_allocator_race.txt

@@ -0,0 +1,3 @@
+  *) mod_http3: Fixed a heap race that crashed the child: worker threads and
+     the event thread allocated from one session allocator that had no mutex.
+     [Alexander Gerasimov <codeguard gmail.com>]

modules/http3/h3_io.c

@@ -285,6 +285,15 @@ static apr_status_t spawn_serviced_session(h3_io_t* io, h3q_conn* conn)
         }
     }
     apr_pool_tag(session_pool, "h3_session");
+    /* Workers allocate from stream subpools while this thread makes its own: share the allocator safely. */
+    apr_thread_mutex_t* alloc_mutex = NULL;
+    if (apr_thread_mutex_create(&alloc_mutex, APR_THREAD_MUTEX_DEFAULT, session_pool) != APR_SUCCESS)
+    {
+        apr_pool_destroy(session_pool);
+        h3q_conn_free(conn);
+        return APR_EGENERAL;
+    }
+    apr_allocator_mutex_set(allocator, alloc_mutex);
 
     h3_session* session = NULL;
     if (h3_session_create(&session, io->server, conn, session_pool) != APR_SUCCESS)

modules/http3/h3_server.c

@@ -54,6 +54,7 @@ static void* APR_THREAD_FUNC port_acquire_thread_fn(apr_thread_t* thread H3_UNUS
     if (apr_pool_create(&ptry, args->pool) != APR_SUCCESS)
     {
         ap_log_error(APLOG_MARK, APLOG_ERR, 0, args->vhost, "port acquirer: could not create a pool");
+        apr_atomic_set32(&port_acquire_running, 0);
         return NULL;
     }
     while (!child_stopping)

modules/http3/h3_stream.c

@@ -126,13 +126,14 @@ void flush_nghttp3(h3_session* session)
         nghttp3_conn_add_ack_offset(session->ngh3, sid, res.accepted);
         if (res.blocked)
         {
-            /* Send buffer full: skip this stream instead of busy-looping on the same vec. */
+            /* Send buffer full: skip this stream instead of busy-looping on the same vec.
+             * Block it again every time: resume_stream reschedules a blocked stream. */
             if (!h3s->write_blocked)
             {
                 h3s->write_blocked = 1;
                 session->blocked_streams++;
-                nghttp3_conn_block_stream(session->ngh3, sid);
             }
+            nghttp3_conn_block_stream(session->ngh3, sid);
             continue;
         }
     }

modules/http3/h3_threads.c

@@ -126,6 +126,10 @@ void* APR_THREAD_FUNC h3_event_thread(apr_thread_t* thread, void* data)
                     h3q_conn_free(conn);
                 }
             }
+        }
+        if (io->thread_running)
+        {
+            /* Also while draining: a pending handshake counts as an MPM connection, so it must finish or time out. */
             progress_pending_handshakes(io);
         }
 

test/modules/http3/test_014_lifecycle.py

@@ -43,9 +43,14 @@ def test_h3_014_04_stop_cleanly(self, env):
         H3Conf(env).add_h3_vhost().install()
         log = env.httpd_error_log
         start = log.current_pos()
+        url = env.mkurl("https", "test1", "/001.html")
         for _ in range(20):
             assert env.apache_restart() == 0
             assert env.wait_udp_port(env.https_port)
+            # a live session, so stop also tears down its control streams
+            r = env.h3_get(url)
+            assert r.exit_code == 0, f"{r}"
+            assert r.response["protocol"] == "HTTP/3", f"{r}"
             assert env.apache_stop() == 0
         # crashed, or still there when the parent gave up waiting
         unclean = [log.RE_ERRLOG_CRASH.pattern, r'.*AH0004[56]: child process']