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systemclock: Don't keep the clock entry locked while getting the time from the clock

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gst_clock_get_time() will take the clock mutex, which would then result in a lock
order violation and possible deadlocks. If both mutexes are to be locked, the
clock must always be locked first.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/7994>
This commit is contained in:
Sebastian Dröge 2024-11-28 16:06:17 +02:00 committed by GStreamer Marge Bot
parent ec698179a9
commit 1ee349f986
1 changed files with 25 additions and 5 deletions
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30
subprojects/gstreamer/gst/gstsystemclock.c
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@ -1126,16 +1126,26 @@ gst_system_clock_id_wait_jitter_unlocked (GstClock * clock,
GstClockReturn status;
gint64 mono_ts;
status = GST_CLOCK_ENTRY_STATUS (entry);
if (G_UNLIKELY (status == GST_CLOCK_UNSCHEDULED)) {
return GST_CLOCK_UNSCHEDULED;
}
/* Getting the time from the clock locks the clock, so without unlocking the
* entry we would have a lock order violation here that can lead to deadlocks.
*
* It's not a problem to take the mutex again after getting the times (which
* might block for a moment) as waiting happens based on the absolute time.
*/
GST_SYSTEM_CLOCK_ENTRY_UNLOCK ((GstClockEntryImpl *) entry);
/* need to call the overridden method because we want to sync against the time
* of the clock, whatever the subclass uses as a clock. */
now = gst_clock_get_time (clock);
mono_ts = g_get_monotonic_time ();
GST_SYSTEM_CLOCK_ENTRY_LOCK ((GstClockEntryImpl *) entry);
/* Might have been unscheduled in the meantime */
status = GST_CLOCK_ENTRY_STATUS (entry);
if (G_UNLIKELY (status == GST_CLOCK_UNSCHEDULED)) {
return GST_CLOCK_UNSCHEDULED;
}
/* get the time of the entry */
entryt = GST_CLOCK_ENTRY_TIME (entry);
@ -1223,10 +1233,20 @@ gst_system_clock_id_wait_jitter_unlocked (GstClock * clock,
"entry %p unlocked after timeout", entry);
}
GST_SYSTEM_CLOCK_ENTRY_UNLOCK ((GstClockEntryImpl *) entry);
/* reschedule if gst_cond_wait_until returned early or we have to reschedule after
* an unlock*/
mono_ts = g_get_monotonic_time ();
now = gst_clock_get_time (clock);
mono_ts = g_get_monotonic_time ();
GST_SYSTEM_CLOCK_ENTRY_LOCK ((GstClockEntryImpl *) entry);
/* Might have been unscheduled in the meantime */
status = GST_CLOCK_ENTRY_STATUS (entry);
if (G_UNLIKELY (status == GST_CLOCK_UNSCHEDULED)) {
goto done;
}
diff = GST_CLOCK_DIFF (now, entryt);
if (diff <= CLOCK_MIN_WAIT_TIME) {