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multiqueue: Fix potential deadlock with parallel release_pad calls

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Commit d3a66f9851 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>
This commit is contained in:
Mart Raudsepp 2022-12-14 23:30:54 +02:00 committed by GStreamer Marge Bot
parent 72884f141c
commit 3fa4ff0562
1 changed files with 7 additions and 5 deletions
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12
subprojects/gstreamer/plugins/elements/gstmultiqueue.c
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@ -1231,6 +1231,12 @@ gst_multi_queue_release_pad (GstElement * element, GstPad * 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)) {
@ -1250,17 +1256,13 @@ gst_multi_queue_release_pad (GstElement * element, GstPad * pad)
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 */
/* 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++;