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gstpad: Recheck pads when linking after temporary unlock

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This commit makes sure that pads are valid for linking
after the pads has been temporarily unlocked in the linking process.
Not doing this opens up for a race condition where
pads potentially can be linked twice.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5678>
This commit is contained in:
Daniel Moberg 2023-11-15 10:03:52 +00:00 committed by Tim-Philipp Müller
parent 15e9b513da
commit 1eca0a1049
1 changed files with 48 additions and 25 deletions
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73
subprojects/gstreamer/gst/gstpad.c
View file

@ -2378,22 +2378,18 @@ wrong_grandparents:
}
}
/* FIXME leftover from an attempt at refactoring... */
/* call with the two pads unlocked, when this function returns GST_PAD_LINK_OK,
* the two pads will be locked in the srcpad, sinkpad order. */
/* check that pads does not have any exisiting links
* and that hierarchy is valid for linking.
*
* The LOCK should be held on both pads
*/
static GstPadLinkReturn
gst_pad_link_prepare (GstPad * srcpad, GstPad * sinkpad, GstPadLinkCheck flags)
gst_pad_link_check_relations (GstPad * srcpad, GstPad * sinkpad,
GstPadLinkCheck flags)
{
GST_CAT_INFO (GST_CAT_PADS, "trying to link %s:%s and %s:%s",
GST_DEBUG_PAD_NAME (srcpad), GST_DEBUG_PAD_NAME (sinkpad));
GST_OBJECT_LOCK (srcpad);
if (G_UNLIKELY (GST_PAD_PEER (srcpad) != NULL))
goto src_was_linked;
GST_OBJECT_LOCK (sinkpad);
if (G_UNLIKELY (GST_PAD_PEER (sinkpad) != NULL))
goto sink_was_linked;
@ -2403,12 +2399,6 @@ gst_pad_link_prepare (GstPad * srcpad, GstPad * sinkpad, GstPadLinkCheck flags)
&& !gst_pad_link_check_hierarchy (srcpad, sinkpad))
goto wrong_hierarchy;
/* check pad caps for non-empty intersection */
if (!gst_pad_link_check_compatible_unlocked (srcpad, sinkpad, flags))
goto no_format;
/* FIXME check pad scheduling for non-empty intersection */
return GST_PAD_LINK_OK;
src_was_linked:
@ -2418,7 +2408,6 @@ src_was_linked:
GST_DEBUG_PAD_NAME (GST_PAD_PEER (srcpad)));
/* we do not emit a warning in this case because unlinking cannot
* be made MT safe.*/
GST_OBJECT_UNLOCK (srcpad);
return GST_PAD_LINK_WAS_LINKED;
}
sink_was_linked:
@ -2428,23 +2417,57 @@ sink_was_linked:
GST_DEBUG_PAD_NAME (GST_PAD_PEER (sinkpad)));
/* we do not emit a warning in this case because unlinking cannot
* be made MT safe.*/
GST_OBJECT_UNLOCK (sinkpad);
GST_OBJECT_UNLOCK (srcpad);
return GST_PAD_LINK_WAS_LINKED;
}
wrong_hierarchy:
{
GST_CAT_INFO (GST_CAT_PADS, "pads have wrong hierarchy");
GST_OBJECT_UNLOCK (sinkpad);
GST_OBJECT_UNLOCK (srcpad);
return GST_PAD_LINK_WRONG_HIERARCHY;
}
no_format:
{
}
/* FIXME leftover from an attempt at refactoring... */
/* call with the two pads unlocked, when this function returns GST_PAD_LINK_OK,
* the two pads will be locked in the srcpad, sinkpad order. */
static GstPadLinkReturn
gst_pad_link_prepare (GstPad * srcpad, GstPad * sinkpad, GstPadLinkCheck flags)
{
GstPadLinkReturn result;
GST_CAT_INFO (GST_CAT_PADS, "trying to link %s:%s and %s:%s",
GST_DEBUG_PAD_NAME (srcpad), GST_DEBUG_PAD_NAME (sinkpad));
GST_OBJECT_LOCK (srcpad);
GST_OBJECT_LOCK (sinkpad);
/* Check pads state, not already linked and correct hierachy. */
result = gst_pad_link_check_relations (srcpad, sinkpad, flags);
if (result != GST_PAD_LINK_OK)
goto unlock_and_return;
/* check pad caps for non-empty intersection */
if (!gst_pad_link_check_compatible_unlocked (srcpad, sinkpad, flags)) {
GST_CAT_INFO (GST_CAT_PADS, "caps are incompatible");
result = GST_PAD_LINK_NOFORMAT;
goto unlock_and_return;
}
/* Need to recheck our pads since gst_pad_link_check_compatible_unlocked might have temporarily unlocked them.
Keeping the first check, because gst_pad_link_check_compatible_unlocked potentially is an expensive operation
which gst_pad_link_check_relations is not. */
result = gst_pad_link_check_relations (srcpad, sinkpad, flags);
if (result != GST_PAD_LINK_OK)
goto unlock_and_return;
/* FIXME check pad scheduling for non-empty intersection */
return GST_PAD_LINK_OK;
unlock_and_return:
{
GST_OBJECT_UNLOCK (sinkpad);
GST_OBJECT_UNLOCK (srcpad);
return GST_PAD_LINK_NOFORMAT;
return result;
}
}