[Bug 735800] New: 1.4.1 regression: Two textoverlay in sequence fail to negotiate

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=735800
  GStreamer | gst-plugins-base | 1.4.1

           Summary: 1.4.1 regression: Two textoverlay in sequence fail to
                    negotiate
    Classification: Platform
           Product: GStreamer
           Version: 1.4.1
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: blocker
          Priority: Normal
         Component: gst-plugins-base
        AssignedTo: gstreamer-bugs at lists.freedesktop.org
        ReportedBy: jan.steffens at gmail.com
         QAContact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---


Created an attachment (id=284990)
 --> (https://bugzilla.gnome.org/attachment.cgi?id=284990)
GST_DEBUG=LOG

With gst-plugins-base 1.4.1, the following pipeline now deadlocks:

gst-launch-1.0 videotestsrc ! textoverlay ! textoverlay ! fakesink

It tries to recursively lock the class' pango_lock.
The (sparse) stack for this is:
g_mutex_lock
gst_base_text_overlay_setcaps
gst_base_text_overlay_video_event (second textoverlay)
gst_pad_push_event
gst_pad_set_caps
gst_base_text_overlay_setcaps
gst_base_text_overlay_video_event (first textoverlay)

With e783a36 applied (which fixes the deadlock), the pipeline fails to
negotiate:

ERROR: from element /GstPipeline:pipeline0/GstVideoTestSrc:videotestsrc0:
Internal data flow error.
Additional debug info:
gstbasesrc.c(2933): gst_base_src_loop ():
/GstPipeline:pipeline0/GstVideoTestSrc:videotestsrc0:
streaming task paused, reason not-negotiated (-4)
ERROR: pipeline doesn't want to preroll.

Log attached.

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