From 1de1e80d5077157fc25503c4699969c57929795d Mon Sep 17 00:00:00 2001
From: Simeon Bird <sbird@andrew.cmu.edu>
Date: Fri, 20 Mar 2015 20:18:46 -0400
Subject: [PATCH] Fix hang on nvidia hardware when deleting sync objects

When a sync object is deleted, the fence it is connected to must already
be signalled, or the driver will busy-wait forever.
Signal fences before deleting syncs to avoid this.

BUG: 343551
FIXED-IN: 5.3
REVIEW: 123090
---
 scene_opengl.cpp | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/scene_opengl.cpp b/scene_opengl.cpp
index 30b113dfd0..1793004c7a 100644
--- a/scene_opengl.cpp
+++ b/scene_opengl.cpp
@@ -123,6 +123,17 @@ SyncObject::SyncObject()
 
 SyncObject::~SyncObject()
 {
+    // If glDeleteSync is called before the xcb fence is signalled
+    // the nvidia driver (the only one to implement GL_SYNC_X11_FENCE_EXT)
+    // deadlocks waiting for the fence to be signalled.
+    // To avoid this, make sure the fence is signalled before
+    // deleting the sync.
+    if (m_state == Resetting || m_state == Ready){
+        trigger();
+        // The flush is necessary!
+        // The trigger command needs to be sent to the X server.
+        xcb_flush(connection());
+    }
     xcb_sync_destroy_fence(connection(), m_fence);
     glDeleteSync(m_sync);