runtime/cgo: add tsan acquire/release around setenv/unsetenv

Change-Id: Iabb25e97714d070c31c657559a97a3bfc979da18
Reviewed-on: https://go-review.googlesource.com/25403
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

misc/cgo/testsanitizers/test.bash

@@ -161,6 +161,9 @@ if test "$tsan" = "yes"; then
 
 	# This test requires rebuilding runtime/cgo with -fsanitize=thread.
 	testtsan tsan6.go "CGO_CFLAGS=-fsanitize=thread CGO_LDFLAGS=-fsanitize=thread" "-installsuffix=tsan"
+
+	# This test requires rebuilding runtime/cgo with -fsanitize=thread.
+	testtsan tsan7.go "CGO_CFLAGS=-fsanitize=thread CGO_LDFLAGS=-fsanitize=thread" "-installsuffix=tsan"
     fi
 fi
 

misc/cgo/testsanitizers/tsan7.go

@@ -0,0 +1,40 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+// Setting an environment variable in a cgo program changes the C
+// environment. Test that this does not confuse the race detector.
+
+/*
+#cgo CFLAGS: -fsanitize=thread
+#cgo LDFLAGS: -fsanitize=thread
+*/
+import "C"
+
+import (
+	"fmt"
+	"os"
+	"sync"
+	"time"
+)
+
+func main() {
+	var wg sync.WaitGroup
+	var mu sync.Mutex
+	f := func() {
+		defer wg.Done()
+		for i := 0; i < 100; i++ {
+			time.Sleep(time.Microsecond)
+			mu.Lock()
+			s := fmt.Sprint(i)
+			os.Setenv("TSAN_TEST"+s, s)
+			mu.Unlock()
+		}
+	}
+	wg.Add(2)
+	go f()
+	go f()
+	wg.Wait()
+}

src/runtime/cgo/gcc_setenv.c

@@ -13,12 +13,16 @@
 void
 x_cgo_setenv(char **arg)
 {
+	_cgo_tsan_acquire();
 	setenv(arg[0], arg[1], 1);
+	_cgo_tsan_release();
 }
 
 /* Stub for calling unsetenv */
 void
 x_cgo_unsetenv(char *arg)
 {
+	_cgo_tsan_acquire();
 	unsetenv(arg);
+	_cgo_tsan_release();
 }