[Bug 783777] New: Deadlock gstpad vs decodebin2

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=783777

            Bug ID: 783777
           Summary: Deadlock gstpad vs decodebin2
    Classification: Platform
           Product: GStreamer
           Version: 1.8.3
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: Normal
         Component: gst-plugins-base
          Assignee: gstreamer-bugs at lists.freedesktop.org
          Reporter: krzysztof.kapuscik at redembedded.com
        QA Contact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---

Created attachment 353730
  --> https://bugzilla.gnome.org/attachment.cgi?id=353730&action=edit
Deadlock callstacks

During dash playback there is an error between pad posting an event (which goes
to decoebin2 on its pad) and decodebin2 trying to modify pad state.

>From the dump (attached):

Thread 21:
#4  0xb69db71a in post_activate (new_mode=GST_PAD_MODE_NONE, pad=0x9430c328) at
/usr/src/debug/gstreamer1.0/1.8.3-r0/gstreamer-1.8.3/gst/gstpad.c:1014

static void
post_activate (GstPad * pad, GstPadMode new_mode)
{
  switch (new_mode) {
    case GST_PAD_MODE_NONE:
      /* ensures that streaming stops */
      GST_PAD_STREAM_LOCK (pad); <====== Hangs here

#23 0xb60261ba in gst_decode_pad_handle_eos (pad=0x9563d9d0) at
/usr/src/debug/gstreamer1.0-plugins-base/1.8.3-r0/gst-plugins-base-1.8.3/gst/playback/gstdecodebin2.c:4156

static gboolean
gst_decode_pad_handle_eos (GstDecodePad * pad)
{
  ...
  EXPOSE_LOCK (dbin);  <====== Lock taken
  if (dbin->decode_chain) {
    drain_and_switch_chains (dbin->decode_chain, pad, &last_group, &drained,
        &switched);

--------------

Thread 17:

#3  0xb6026164 in gst_decode_pad_handle_eos (pad=0x9563d6c0) at
/usr/src/debug/gstreamer1.0-plugins-base/1.8.3-r0/gst-plugins-base-1.8.3/gst/playback/gstdecodebin2.c:4154

static gboolean
gst_decode_pad_handle_eos (GstDecodePad * pad)
{
....

  GST_LOG_OBJECT (dbin, "pad %p", pad);
  EXPOSE_LOCK (dbin); <========= Waits for lock here

#16 0xb69d6ab4 in gst_pad_send_event_unchecked (pad=pad at entry=0x9430c328,
event=event at entry=0x9430f930, type=<optimized out>,
type at entry=GST_PAD_PROBE_TYPE_EVENT_DOWNSTREAM) at
/usr/src/debug/gstreamer1.0/1.8.3-r0/gstreamer-1.8.3/gst/gstpad.c:5587

        /* lock order: STREAM_LOCK, LOCK, recheck flushing. */
        GST_OBJECT_UNLOCK (pad);
        GST_PAD_STREAM_LOCK (pad); <===== Lock taken here, as EOS event is
serialized
        need_unlock = TRUE;
        GST_OBJECT_LOCK (pad);
        if (G_UNLIKELY (GST_PAD_IS_FLUSHING (pad)))
          goto flushing;

        if (G_UNLIKELY (GST_PAD_IS_EOS (pad)))
          goto eos;
      }
      break;
  }

  /* now do the probe */
  PROBE_PUSH (pad,
      type | GST_PAD_PROBE_TYPE_PUSH |
      GST_PAD_PROBE_TYPE_BLOCK, event, probe_stopped);

  PROBE_PUSH (pad, type | GST_PAD_PROBE_TYPE_PUSH, event, probe_stopped);

  eventfullfunc = GST_PAD_EVENTFULLFUNC (pad);
  eventfunc = GST_PAD_EVENTFUNC (pad);
  if (G_UNLIKELY (eventfunc == NULL && eventfullfunc == NULL))
    goto no_function;

  ACQUIRE_PARENT (pad, parent, no_parent);
  GST_OBJECT_UNLOCK (pad);

  ret = pre_eventfunc_check (pad, event); <= executes this 

(gdb) print *event
$5 = {mini_object = {type = 3052471832, refcount = 54, lockstate = 0, flags =
0, copy = 0xb69c6751 <_gst_event_copy>, dispose = 0x0, free = 0xb69c68bd
<_gst_event_free>, n_qdata = 0, qdata = 0x0}, type = GST_EVENT_EOS, timestamp =
18446744073709551615, seqnum = 8629}

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