Try to make SCULPT_orig_vert_data_init avoid allocating undo nodes,

which calls into BMLog which, while now threadsafe (ish?) causes
threads to get bogged down in lock contention.

source/blender/blenkernel/intern/pbvh_bmesh.c

@@ -911,11 +911,29 @@ static bool edge_queue_tri_in_sphere(const EdgeQueue *q, BMFace *f)
 
   /* Get closest point in triangle to sphere center */
   BM_face_as_array_vert_tri(f, v_tri);
+#if 0
+  /*
+  closest_on_tri_to_point_v3 is being slow
+  */
 
+  float mindis = 1e17;
+  float dis;
+  copy_v3_v3(c, q->center);
+
+  for (int i=0; i<3; i++) {
+    dis = len_squared_v3v3(v_tri[i]->co, c);
+    mindis = MIN2(mindis, dis);
+
+    dis = dist_squared_to_line_segment_v3(c, v_tri[i]->co, v_tri[(i+1)%3]->co);
+    mindis = MIN2(mindis, dis);
+  }
+  return mindis <= q->radius_squared;
+#else
   closest_on_tri_to_point_v3(c, q->center, v_tri[0]->co, v_tri[1]->co, v_tri[2]->co);
 
   /* Check if triangle intersects the sphere */
   return len_squared_v3v3(q->center, c) <= q->radius_squared;
+#endif
 }
 
 static bool edge_queue_tri_in_circle(const EdgeQueue *q, BMFace *f)
@@ -2584,7 +2602,7 @@ void BKE_pbvh_build_bmesh(PBVH *pbvh,
   pbvh->cd_vcol_offset = CustomData_get_offset(&bm->vdata, CD_PROP_COLOR);
 
   /* TODO: choose leaf limit better */
-  pbvh->leaf_limit = 3000;
+  pbvh->leaf_limit = 1000;
 
   BMIter iter;
   BMVert *v;

source/blender/editors/sculpt_paint/sculpt.c

@@ -1332,6 +1332,7 @@ void SCULPT_orig_vert_data_unode_init(SculptOrigVertData *data, Object *ob, Scul
     data->bm_log = ss->bm_log;
   }
   else {
+    data->datatype = data->unode->type;
     data->coords = data->unode->co;
     data->normals = data->unode->no;
     data->vmasks = data->unode->mask;
@@ -1345,10 +1346,15 @@ void SCULPT_orig_vert_data_unode_init(SculptOrigVertData *data, Object *ob, Scul
  */
 void SCULPT_orig_vert_data_init(SculptOrigVertData *data, Object *ob, PBVHNode *node)
 {
-  SculptUndoNode *unode;
+  SculptUndoNode *unode = NULL;
   data->ss = ob->sculpt;
-  unode = SCULPT_undo_push_node(ob, node, SCULPT_UNDO_COORDS);
+
+  if (!ob->sculpt->bm) {
+    unode = SCULPT_undo_push_node(ob, node, SCULPT_UNDO_COORDS);
+  }
+
   SCULPT_orig_vert_data_unode_init(data, ob, unode);
+  data->datatype = SCULPT_UNDO_COORDS;
 }
 
 /**
@@ -1356,7 +1362,7 @@ void SCULPT_orig_vert_data_init(SculptOrigVertData *data, Object *ob, PBVHNode *
  */
 void SCULPT_orig_vert_data_update(SculptOrigVertData *orig_data, PBVHVertexIter *iter)
 {
-  if (orig_data->unode->type == SCULPT_UNDO_COORDS) {
+  if (orig_data->datatype == SCULPT_UNDO_COORDS) {
     if (orig_data->bm_log) {
       orig_data->co = BM_ELEM_CD_GET_VOID_P(iter->bm_vert, orig_data->ss->cd_origco_offset);
 
@@ -1376,7 +1382,7 @@ void SCULPT_orig_vert_data_update(SculptOrigVertData *orig_data, PBVHVertexIter
       orig_data->no = orig_data->normals[iter->i];
     }
   }
-  else if (orig_data->unode->type == SCULPT_UNDO_COLOR) {
+  else if (orig_data->datatype == SCULPT_UNDO_COLOR) {
     if (orig_data->bm_log) {
       orig_data->col = BM_ELEM_CD_GET_VOID_P(iter->bm_vert, orig_data->ss->cd_origvcol_offset);
 
@@ -1386,7 +1392,7 @@ void SCULPT_orig_vert_data_update(SculptOrigVertData *orig_data, PBVHVertexIter
       orig_data->col = orig_data->colors[iter->i];
     }
   }
-  else if (orig_data->unode->type == SCULPT_UNDO_MASK) {
+  else if (orig_data->datatype == SCULPT_UNDO_MASK) {
     if (orig_data->bm_log) {
       orig_data->mask = BM_log_original_mask(orig_data->bm_log, iter->bm_vert);
     }

source/blender/editors/sculpt_paint/sculpt_intern.h

@@ -226,6 +226,7 @@ typedef struct {
   struct BMLog *bm_log;
 
   struct SculptUndoNode *unode;
+  int datatype;
   float (*coords)[3];
   short (*normals)[3];
   const float *vmasks;

source/blender/editors/sculpt_paint/sculpt_paint_color.c

@@ -124,6 +124,7 @@ static void do_paint_brush_task_cb_ex(void *__restrict userdata,
 
   SculptOrigVertData orig_data;
   SCULPT_orig_vert_data_init(&orig_data, data->ob, data->nodes[n]);
+  orig_data.datatype = SCULPT_UNDO_COLOR;
 
   color_buffer = BKE_pbvh_node_color_buffer_get(data->nodes[n]);
 

source/blender/gpu/intern/gpu_buffers.c

@@ -932,6 +932,7 @@ void GPU_pbvh_update_attribute_names(CustomData *vdata, CustomData *ldata)
       cl += cl->active;
 
       DRW_make_cdlayer_attr_aliases(&g_vbo_id.format, "c", vdata, cl);
+      GPU_vertformat_alias_add(&g_vbo_id.format, "ac");
     }
 
     g_vbo_id.fset = GPU_vertformat_attr_add(