putMVar and takeMVar: add write_barrier() to fix race with throwTo

diff --git a/rts/PrimOps.cmm b/rts/PrimOps.cmm
index 40948a3..dc60ff2 100644 (file)
--- a/rts/PrimOps.cmm
+++ b/rts/PrimOps.cmm
@@ -1651,8 +1651,11 @@ takeMVarzh_fast
                                    CurrentTSO) [];
        }
        StgTSO__link(CurrentTSO)       = stg_END_TSO_QUEUE_closure;
-       StgTSO_why_blocked(CurrentTSO) = BlockedOnMVar::I16;
        StgTSO_block_info(CurrentTSO)  = mvar;
+        // write barrier for throwTo(), which looks at block_info
+        // if why_blocked==BlockedOnMVar.
+        prim %write_barrier() [];
+       StgTSO_why_blocked(CurrentTSO) = BlockedOnMVar::I16;
        StgMVar_tail(mvar) = CurrentTSO;
        
         R1 = mvar;
@@ -1808,8 +1811,11 @@ putMVarzh_fast
                                    CurrentTSO) [];
        }
        StgTSO__link(CurrentTSO)       = stg_END_TSO_QUEUE_closure;
-       StgTSO_why_blocked(CurrentTSO) = BlockedOnMVar::I16;
        StgTSO_block_info(CurrentTSO)  = mvar;
+        // write barrier for throwTo(), which looks at block_info
+        // if why_blocked==BlockedOnMVar.
+        prim %write_barrier() [];
+       StgTSO_why_blocked(CurrentTSO) = BlockedOnMVar::I16;
        StgMVar_tail(mvar) = CurrentTSO;
        
         R1 = mvar;