u_threaded_gallium: remove synchronization in fence_server_sync

The whole point of fence_server_sync is that it can be used to
avoid waiting in the application thread.

Reviewed-by: Andres Rodriguez <andresx7@gmail.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>

src/gallium/auxiliary/util/u_threaded_context.c

@@ -1834,15 +1834,23 @@ tc_create_fence_fd(struct pipe_context *_pipe,
    pipe->create_fence_fd(pipe, fence, fd);
 }
 
+static void
+tc_call_fence_server_sync(struct pipe_context *pipe, union tc_payload *payload)
+{
+   pipe->fence_server_sync(pipe, payload->fence);
+   pipe->screen->fence_reference(pipe->screen, &payload->fence, NULL);
+}
+
 static void
 tc_fence_server_sync(struct pipe_context *_pipe,
                      struct pipe_fence_handle *fence)
 {
    struct threaded_context *tc = threaded_context(_pipe);
-   struct pipe_context *pipe = tc->pipe;
+   struct pipe_screen *screen = tc->pipe->screen;
+   union tc_payload *payload = tc_add_small_call(tc, TC_CALL_fence_server_sync);
 
-   tc_sync(tc);
-   pipe->fence_server_sync(pipe, fence);
+   payload->fence = NULL;
+   screen->fence_reference(screen, &payload->fence, fence);
 }
 
 static struct pipe_video_codec *

src/gallium/auxiliary/util/u_threaded_context.h

@@ -309,6 +309,7 @@ union tc_payload {
    struct pipe_query *query;
    struct pipe_resource *resource;
    struct pipe_transfer *transfer;
+   struct pipe_fence_handle *fence;
    uint64_t handle;
 };
 

src/gallium/auxiliary/util/u_threaded_context_calls.h

@@ -1,5 +1,6 @@
 CALL(flush)
 CALL(callback)
+CALL(fence_server_sync)
 CALL(destroy_query)
 CALL(begin_query)
 CALL(end_query)