From a8a8e6b797e7f5d0e35a9b1d59533fa50fac3607 Mon Sep 17 00:00:00 2001
From: Jakob Gruber <jgruber@chromium.org>
Date: Wed, 21 Apr 2021 08:43:50 +0200
Subject: [PATCH] Remove FlagScope use in test-js-to-wasm.cc

Flag reads from background threads are unfortunately scattered and
hard to completely avoid in the current state of V8. An example TSAN
failure:

ci.chromium.org/ui/p/v8/builders/ci/V8%20Linux64%20TSAN/36369/overview

The root cause is that FlagScope destruction modifies flag values on
the main thread, racing with flag reads from the background thread. In
cctests, there's no need to reset flags back to initial values at the
end of tests. Let's simply remove the problematic flag scopes.

Bug: v8:11658
Change-Id: I59ed3794ddc9ed570772726a423dc22afc4dc207
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2843346
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74082}
---
 test/cctest/test-js-to-wasm.cc | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/test/cctest/test-js-to-wasm.cc b/test/cctest/test-js-to-wasm.cc
index e1734162e8..21cfa77b21 100644
--- a/test/cctest/test-js-to-wasm.cc
+++ b/test/cctest/test-js-to-wasm.cc
@@ -262,12 +262,13 @@ enum TestMode { kJSToWasmInliningDisabled, kJSToWasmInliningEnabled };
 class FastJSWasmCallTester {
  public:
   FastJSWasmCallTester()
-      : allow_natives_syntax_(&i::FLAG_allow_natives_syntax, true),
-        inline_js_wasm_calls_(&i::FLAG_turbo_inline_js_wasm_calls, true),
-        stress_background_compile_(&i::FLAG_stress_background_compile, false),
-        allocator_(),
+      : allocator_(),
         zone_(&allocator_, ZONE_NAME),
-        builder_(zone_.New<WasmModuleBuilder>(&zone_)) {}
+        builder_(zone_.New<WasmModuleBuilder>(&zone_)) {
+    i::FLAG_allow_natives_syntax = true;
+    i::FLAG_turbo_inline_js_wasm_calls = true;
+    i::FLAG_stress_background_compile = false;
+  }
 
   void DeclareCallback(const char* name, FunctionSig* signature,
                        const char* module) {
@@ -742,9 +743,6 @@ class FastJSWasmCallTester {
     return string_stream.str();
   }
 
-  i::FlagScope<bool> allow_natives_syntax_;
-  i::FlagScope<bool> inline_js_wasm_calls_;
-  i::FlagScope<bool> stress_background_compile_;
   AccountingAllocator allocator_;
   Zone zone_;
   WasmModuleBuilder* builder_;