Fix T47008: OSL Memory Corruption (Use after free)

The issue was caused by OSL using TLS which is required to be freed before the
Cycles session is freed. This is quite tricky to do in Cycles because different
render session are sharing the same task scheduler, so when one session is being
freed TLS might need to be active still.

In order to solve this, we are now doing JIT optimization ahead of the time
which ensures either TLS of JIT is freed before the render on multi-core system
or freed on OSLRenderSession destroy on single-core system.

This might increase synchronization time due to JIT of unused function, but
that we can solve later with some smart idea,

1 files changed, 13 insertions, 3 deletions

diff --git a/intern/cycles/render/osl.cpp b/intern/cycles/render/osl.cpp
index 4933ed6c613..e5842c796db 100644
--- a/intern/cycles/render/osl.cpp
+++ b/intern/cycles/render/osl.cpp
@@ -125,11 +125,21 @@ void OSLShaderManager::device_update(Device *device, DeviceScene *dscene, Scene
 
 	device_update_common(device, dscene, scene, progress);
 
-	/* greedyjit test
 	{
+		/* Perform greedyjit optimization.
+		 *
+		 * This might waste time on optimizing gorups which are never actually
+		 * used, but this prevents OSL from allocating data on TLS at render
+		 * time.
+		 *
+		 * This is much better for us because this way we aren't required to
+		 * stop task scheduler threads to make sure all TLS is clean and don't
+		 * have issues with TLS data free accessing freed memory if task scheduler
+		 * is being freed after the Session is freed.
+		 */
 		thread_scoped_lock lock(ss_shared_mutex);
 		ss->optimize_all_groups();
-	}*/
+	}
 }
 
 void OSLShaderManager::device_free(Device *device, DeviceScene *dscene, Scene *scene)
@@ -195,7 +205,7 @@ void OSLShaderManager::shading_system_init()
 		ss_shared->attribute("lockgeom", 1);
 		ss_shared->attribute("commonspace", "world");
 		ss_shared->attribute("searchpath:shader", path_get("shader"));
-		//ss_shared->attribute("greedyjit", 1);
+		ss_shared->attribute("greedyjit", 1);
 
 		VLOG(1) << "Using shader search path: " << path_get("shader");