From c0f0e2ca6f3fc0aefab93542211e01bc61be8f34 Mon Sep 17 00:00:00 2001
From: Brecht Van Lommel <brecht@blender.org>
Date: Tue, 18 Feb 2025 16:20:59 +0100
Subject: [PATCH] Fix #129596: Cycles oneAPI crash with interactive BVH updates

There is a bug in Embree that makes BVH updates crash. Disabling multithreaded
BVH updates after the initial BVH build appears to work around it, at the cost
of some performance.

This will not affect performance of the initial BVH build, transforming objects
or editing a single mesh. It will only affect performance when multiple smaller
meshes are edited together, as those can no longer have their BVH updated in
parallel or benefit from parallellization over many primitives.

Pull Request: https://projects.blender.org/blender/blender/pulls/134747
---
 intern/cycles/device/device.cpp  | 13 +++++++++++++
 intern/cycles/device/device.h    |  2 ++
 intern/cycles/scene/geometry.cpp | 14 ++++++++++++--
 intern/cycles/scene/geometry.h   |  1 +
 4 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/intern/cycles/device/device.cpp b/intern/cycles/device/device.cpp
index cf77f76bec6..44fa7988f2a 100644
--- a/intern/cycles/device/device.cpp
+++ b/intern/cycles/device/device.cpp
@@ -816,4 +816,17 @@ bool GPUDevice::is_shared(const void *shared_pointer,
 
 /* DeviceInfo */
 
+bool DeviceInfo::contains_device_type(const DeviceType type) const
+{
+  if (this->type == type) {
+    return true;
+  }
+  for (const DeviceInfo &info : multi_devices) {
+    if (info.contains_device_type(type)) {
+      return true;
+    }
+  }
+  return false;
+}
+
 CCL_NAMESPACE_END
diff --git a/intern/cycles/device/device.h b/intern/cycles/device/device.h
index 8912000f788..f55fa3f7f18 100644
--- a/intern/cycles/device/device.h
+++ b/intern/cycles/device/device.h
@@ -130,6 +130,8 @@ class DeviceInfo {
   {
     return !(*this == info);
   }
+
+  bool contains_device_type(const DeviceType type) const;
 };
 
 /* Device */
diff --git a/intern/cycles/scene/geometry.cpp b/intern/cycles/scene/geometry.cpp
index d51e7c6270c..7443dbbd8f2 100644
--- a/intern/cycles/scene/geometry.cpp
+++ b/intern/cycles/scene/geometry.cpp
@@ -943,13 +943,23 @@ void GeometryManager::device_update(Device *device,
     });
     TaskPool pool;
 
+    /* Work around Embree/oneAPI bug #129596 with BVH updates. */
+    const bool use_multithreaded_build = first_bvh_build ||
+                                         !device->info.contains_device_type(DEVICE_ONEAPI);
+    first_bvh_build = false;
+
     size_t i = 0;
     for (Geometry *geom : scene->geometry) {
       if (geom->is_modified() || geom->need_update_bvh_for_offset) {
         need_update_scene_bvh = true;
-        pool.push([geom, device, dscene, scene, &progress, i, num_bvh] {
+        if (use_multithreaded_build) {
+          pool.push([geom, device, dscene, scene, &progress, i, num_bvh] {
+            geom->compute_bvh(device, dscene, &scene->params, &progress, i, num_bvh);
+          });
+        }
+        else {
           geom->compute_bvh(device, dscene, &scene->params, &progress, i, num_bvh);
-        });
+        }
         if (geom->need_build_bvh(bvh_layout)) {
           i++;
         }
diff --git a/intern/cycles/scene/geometry.h b/intern/cycles/scene/geometry.h
index 4b57d7fa692..6144bf19c83 100644
--- a/intern/cycles/scene/geometry.h
+++ b/intern/cycles/scene/geometry.h
@@ -225,6 +225,7 @@ class GeometryManager {
 
   /* Update Flags */
   bool need_flags_update;
+  bool first_bvh_build = true;
 
   /* Constructor/Destructor */
   GeometryManager();