[project @ 2005-10-12 12:58:38 by simonmar]

DEBUG_FILL_SLOP: don't do anything on SMP, zeroing slop words isn't safe

diff --git a/ghc/includes/Updates.h b/ghc/includes/Updates.h
index 0d0bf2f..2685850 100644 (file)
--- a/ghc/includes/Updates.h
+++ b/ghc/includes/Updates.h
@@ -185,8 +185,13 @@ extern void awakenBlockedQueue(StgBlockingQueueElement *q, StgClosure *node);
  * to point to itself, and the closure being updated should not
  * already have been updated (the mutable list will get messed up
  * otherwise).
+ *
+ * NB. We do *not* do this in SMP mode, because when we have the
+ * possibility of multiple threads entering the same closure, zeroing
+ * the slop in one of the threads would have a disastrous effect on
+ * the other (seen in the wild!).
  */
-#if !defined(DEBUG)
+#if !defined(DEBUG) || defined(SMP)
 
 #define DEBUG_FILL_SLOP(p) /* nothing */