From: Ivan Maidanski <ivmai@mail.ru>
Date: Fri, 1 Dec 2017 08:48:08 +0000 (+0300)
Subject: Workaround TSan warning about data race in generic_malloc_many
X-Git-Tag: v8.0.0~465
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=31cc9697e40ad05bf92b9570211ad4dd902fc0cc;p=gc

Workaround TSan warning about data race in generic_malloc_many

It is acceptable to update GC_bytes_found counter without
synchronization (so, it is OK to have inaccurate value in
GC_bytes_found in favor of performance).

* mallocx.c [PARALLEL_MARK && THREAD_SANITIZER]
(GC_generic_malloc_many): Acquire the allocation lock to update
GC_bytes_found (after successful GC_reclaim_generic).
* mallocx.c [PARALLEL_MARK && !THREAD_SANITIZER]
(GC_generic_malloc_many): Move GC_bytes_found update into the block
executed with the mark lock held.
---

diff --git a/mallocx.c b/mallocx.c
index a38653c9..242804a6 100644
--- a/mallocx.c
+++ b/mallocx.c
@@ -357,11 +357,6 @@ GC_API void GC_CALL GC_generic_malloc_many(size_t lb, int k, void **result)
             op = GC_reclaim_generic(hbp, hhdr, lb,
                                     ok -> ok_init, 0, &my_bytes_allocd);
             if (op != 0) {
-              /* We also reclaimed memory, so we need to adjust         */
-              /* that count.                                            */
-              /* This should be atomic, so the results may be           */
-              /* inaccurate.                                            */
-              GC_bytes_found += my_bytes_allocd;
 #             ifdef PARALLEL_MARK
                 if (GC_parallel) {
                   *result = op;
@@ -370,11 +365,23 @@ GC_API void GC_CALL GC_generic_malloc_many(size_t lb, int k, void **result)
                   GC_acquire_mark_lock();
                   -- GC_fl_builder_count;
                   if (GC_fl_builder_count == 0) GC_notify_all_builder();
-                  GC_release_mark_lock();
+#                 ifdef THREAD_SANITIZER
+                    GC_release_mark_lock();
+                    LOCK();
+                    GC_bytes_found += my_bytes_allocd;
+                    UNLOCK();
+#                 else
+                    GC_bytes_found += my_bytes_allocd;
+                                        /* The result may be inaccurate. */
+                    GC_release_mark_lock();
+#                 endif
                   (void) GC_clear_stack(0);
                   return;
                 }
 #             endif
+              /* We also reclaimed memory, so we need to adjust       */
+              /* that count.                                          */
+              GC_bytes_found += my_bytes_allocd;
               GC_bytes_allocd += my_bytes_allocd;
               goto out;
             }