Commit
d3a66f9851ea introduced a potential deadlock with two parallel release_pad
calls, where one could release the main multiqueue lock (qlock) while still
holding the reconf_lock and then calling other routines which in some conditions
may try to acquire qlock again. The second release_pad could already acquire the
qlock and then start waiting on reconf_lock, which may never be possible because
because the first one isn't releasing it until it can acquire qlock.
Fix it by holding reconf_lock for the whole durationg of qlock, making this
particular deadlock impossible.
Fixes #1642
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/3571>
GST_LOG_OBJECT (element, "pad %s:%s", GST_DEBUG_PAD_NAME (pad));
GST_LOG_OBJECT (element, "pad %s:%s", GST_DEBUG_PAD_NAME (pad));
+ /* Take the reconfiguration lock before the qlock to avoid deadlocks
+ * from two release_pad running in parallel on different mqueue slots.
+ * We need reconf_lock for removing the singlequeue from the list, to
+ * prevent overlapping release/request from causing problems */
+ g_mutex_lock (&mqueue->reconf_lock);
+
GST_MULTI_QUEUE_MUTEX_LOCK (mqueue);
/* Find which single queue it belongs to, knowing that it should be a sinkpad */
for (tmp = mqueue->queues; tmp; tmp = g_list_next (tmp)) {
GST_MULTI_QUEUE_MUTEX_LOCK (mqueue);
/* Find which single queue it belongs to, knowing that it should be a sinkpad */
for (tmp = mqueue->queues; tmp; tmp = g_list_next (tmp)) {
gst_clear_object (&srcpad);
GST_WARNING_OBJECT (mqueue, "That pad doesn't belong to this element ???");
GST_MULTI_QUEUE_MUTEX_UNLOCK (mqueue);
gst_clear_object (&srcpad);
GST_WARNING_OBJECT (mqueue, "That pad doesn't belong to this element ???");
GST_MULTI_QUEUE_MUTEX_UNLOCK (mqueue);
+ g_mutex_unlock (&mqueue->reconf_lock);
return;
}
/* FIXME: The removal of the singlequeue should probably not happen until it
* finishes draining */
return;
}
/* FIXME: The removal of the singlequeue should probably not happen until it
* finishes draining */
- /* Take the reconfiguration lock before removing the singlequeue from
- * the list, to prevent overlapping release/request from causing
- * problems */
- g_mutex_lock (&mqueue->reconf_lock);
-
/* remove it from the list */
mqueue->queues = g_list_delete_link (mqueue->queues, tmp);
mqueue->queues_cookie++;
/* remove it from the list */
mqueue->queues = g_list_delete_link (mqueue->queues, tmp);
mqueue->queues_cookie++;