Eliminate TSan warning about data race when accessing GC_debugging_started

Now GC_debugging_started variable is double-checked with the allocation
lock held before calling GC_start_debugging_inner.

* dbg_mlc.c (GC_start_debugging_inner): Define as GC_INNER (instead of
STATIC).
* dbg_mlc.c [THREADS] (GC_start_debugging): Define as STATIC; do not
call GC_start_debugging_inner() if GC_debugging_started.
* dbg_mlc.c [!THREADS] (GC_start_debugging): Define as macro (redirect
to GC_start_debugging_inner).
* gcj_mlc.c (GC_debug_gcj_malloc): Call GC_start_debugging_inner
(holding the lock) instead of GC_start_debugging.
* include/private/gc_priv.h (GC_start_debugging): Rename to
GC_start_debugging_inner; improve usage comment.

1 files changed, 13 insertions, 8 deletions

diff --git a/dbg_mlc.c b/dbg_mlc.c
index c22435ae..085ba2e7 100644
--- a/dbg_mlc.c
+++ b/dbg_mlc.c
@@ -465,7 +465,7 @@ STATIC void GC_debug_print_heap_obj_proc(ptr_t p)
   STATIC void GC_do_nothing(void) {}
 #endif
 
-STATIC void GC_start_debugging_inner(void)
+GC_INNER void GC_start_debugging_inner(void)
 {
   GC_ASSERT(I_HOLD_LOCK());
 # ifndef SHORT_DBG_HDRS
@@ -480,14 +480,19 @@ STATIC void GC_start_debugging_inner(void)
   GC_register_displacement_inner((word)sizeof(oh));
 }
 
-GC_INNER void GC_start_debugging(void)
-{
-  DCL_LOCK_STATE;
+#ifdef THREADS
+  STATIC void GC_start_debugging(void)
+  {
+    DCL_LOCK_STATE;
 
-  LOCK();
-  GC_start_debugging_inner();
-  UNLOCK();
-}
+    LOCK();
+    if (!GC_debugging_started)
+      GC_start_debugging_inner();
+    UNLOCK();
+  }
+#else
+# define GC_start_debugging GC_start_debugging_inner
+#endif /* !THREADS */
 
 size_t GC_debug_header_size = sizeof(oh);