From: Marc-André Lureau <marcandre.lureau@redhat.com>

Fixes a deadlock where the backend calls QEMU, while QEMU also calls the
backend simultaneously, both ends waiting for each other.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 contrib/vhost-user-gpu/vhost-user-gpu.c | 32 ++++++++++++++++++++-----
 1 file changed, 26 insertions(+), 6 deletions(-)

diff --git a/contrib/vhost-user-gpu/vhost-user-gpu.c b/contrib/vhost-user-gpu/vhost-user-gpu.c
index 7dcc02966c..810e227382 100644
--- a/contrib/vhost-user-gpu/vhost-user-gpu.c
+++ b/contrib/vhost-user-gpu/vhost-user-gpu.c
@@ -261,10 +261,32 @@ vg_ctrl_response_nodata(VuGpu *g,
     vg_ctrl_response(g, cmd, &resp, sizeof(resp));
 }
 
+
+static gboolean
+get_display_info_cb(gint fd, GIOCondition condition, gpointer user_data)
+{
+    struct virtio_gpu_resp_display_info dpy_info = { {} };
+    VuGpu *vg = user_data;
+    struct virtio_gpu_ctrl_command *cmd = QTAILQ_LAST(&vg->fenceq);
+
+    g_debug("disp info cb");
+    assert(cmd->cmd_hdr.type == VIRTIO_GPU_CMD_GET_DISPLAY_INFO);
+    if (!vg_recv_msg(vg, VHOST_USER_GPU_GET_DISPLAY_INFO, sizeof(dpy_info), &dpy_info)) {
+        return G_SOURCE_CONTINUE;
+    }
+
+    QTAILQ_REMOVE(&vg->fenceq, cmd, next);
+    vg_ctrl_response(vg, cmd, &dpy_info.hdr, sizeof(dpy_info));
+
+    vg->wait_in = 0;
+    vg_handle_ctrl(&vg->dev.parent, 0);
+
+    return G_SOURCE_REMOVE;
+}
+
 void
 vg_get_display_info(VuGpu *vg, struct virtio_gpu_ctrl_command *cmd)
 {
-    struct virtio_gpu_resp_display_info dpy_info = { {} };
     VhostUserGpuMsg msg = {
         .request = VHOST_USER_GPU_GET_DISPLAY_INFO,
         .size = 0,
@@ -273,11 +295,9 @@ vg_get_display_info(VuGpu *vg, struct virtio_gpu_ctrl_command *cmd)
     assert(vg->wait_in == 0);
 
     vg_send_msg(vg, &msg, -1);
-    if (!vg_recv_msg(vg, msg.request, sizeof(dpy_info), &dpy_info)) {
-        return;
-    }
-
-    vg_ctrl_response(vg, cmd, &dpy_info.hdr, sizeof(dpy_info));
+    vg->wait_in = g_unix_fd_add(vg->sock_fd, G_IO_IN | G_IO_HUP,
+                               get_display_info_cb, vg);
+    cmd->state = VG_CMD_STATE_PENDING;
 }
 
 static void
-- 
2.29.0