calling g_source_add_child_source(parentsrc, childsrc) causes a segfault in block_source(childsrc) when childsrc has at least one child source and parentsrc happens to be blocked at the time.

In my case the code that triggers the segfault looks like:

    writesrc =
        g_pollable_output_stream_create_source (G_POLLABLE_OUTPUT_STREAM
        (watch->conn->output_stream), NULL);
    g_source_set_callback (writesrc,
        (GSourceFunc) gst_rtsp_source_dispatch_write, watch, NULL);
    g_source_add_child_source ((GSource *) watch, writesrc);

And the backtrace:

+ Trace 232635

I see the failure in glib 3.26 but i don't think that has changed on git master.