[zone-stats] Fix race-condition when reading Zone stats across threads

Bug: v8:12639
Change-Id: I10aaa576fdc84d848aa28ed8e07d5793a0954ff1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3472023Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79173}

src/zone/zone.cc

@@ -39,8 +39,7 @@ Zone::Zone(AccountingAllocator* allocator, const char* name,
 
 Zone::~Zone() {
   DeleteAll();
-
-  DCHECK_EQ(segment_bytes_allocated_, 0);
+  DCHECK_EQ(segment_bytes_allocated_.load(), 0);
 }
 
 void* Zone::AsanNew(size_t size) {

src/zone/zone.h

@@ -198,12 +198,12 @@ class V8_EXPORT_PRIVATE Zone final {
   static const size_t kMaximumSegmentSize = 32 * KB;
 
   // The number of bytes allocated in this zone so far.
-  size_t allocation_size_ = 0;
+  std::atomic<size_t> allocation_size_ = {0};
 
   // The number of bytes allocated in segments.  Note that this number
   // includes memory allocated from the OS but not yet allocated from
   // the zone.
-  size_t segment_bytes_allocated_ = 0;
+  std::atomic<size_t> segment_bytes_allocated_ = {0};
 
   // Expand the Zone to hold at least 'size' more bytes and allocate
   // the bytes. Returns the address of the newly allocated chunk of
@@ -226,10 +226,10 @@ class V8_EXPORT_PRIVATE Zone final {
 
 #ifdef V8_ENABLE_PRECISE_ZONE_STATS
   TypeStats type_stats_;
-  size_t allocation_size_for_tracing_ = 0;
+  std::atomic<size_t> allocation_size_for_tracing_ = {0};
 
   // The number of bytes freed in this zone so far.
-  size_t freed_size_for_tracing_ = 0;
+  stdd::atomic<size_t> freed_size_for_tracing_ = {0};
 #endif
 
   friend class ZoneScope;