From 701858e81bff8032262f56b753c7f90facd2ee27 Mon Sep 17 00:00:00 2001
From: Ivan Maidanski <ivmai@mail.ru>
Date: Wed, 7 Mar 2018 20:40:05 +0300
Subject: [PATCH] Avoid potential race when storing oh_back_ptr during parallel
 marking

* dbg_mlc.c [KEEP_BACK_PTRS && PARALLEL_MARK] (GC_store_back_pointer):
Store source to dest->oh_back_ptr atomically (unordered atomic store
is sufficient here).
---
 dbg_mlc.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/dbg_mlc.c b/dbg_mlc.c
index 492a3d4c..610728da 100644
--- a/dbg_mlc.c
+++ b/dbg_mlc.c
@@ -90,7 +90,12 @@
   GC_INNER void GC_store_back_pointer(ptr_t source, ptr_t dest)
   {
     if (GC_HAS_DEBUG_INFO(dest)) {
-      ((oh *)dest) -> oh_back_ptr = HIDE_BACK_PTR(source);
+#     ifdef PARALLEL_MARK
+        AO_store((volatile AO_t *)&((oh *)dest)->oh_back_ptr,
+                 (AO_t)HIDE_BACK_PTR(source));
+#     else
+        ((oh *)dest) -> oh_back_ptr = HIDE_BACK_PTR(source);
+#     endif
     }
   }
 
-- 
2.40.0