runtime/cgo: add TSAN acquire/release calls

Add TSAN acquire/release calls to runtime/cgo to match the ones
generated by cgo.  This avoids a false positive race around the malloc
memory used in runtime/cgo when other goroutines are simultaneously
calling malloc and free from cgo.

These new calls will only be used when building with CGO_CFLAGS and
CGO_LDFLAGS set to -fsanitize=thread, which becomes a requirement to
avoid all false positives when using TSAN.  These are needed not just
for runtime/cgo, but also for any runtime package that uses cgo (such as
net and os/user).

Add an unused attribute to the _cgo_tsan_acquire and _cgo_tsan_release
functions, in case there are no actual cgo function calls.

Add a test that checks that setting CGO_CFLAGS/CGO_LDFLAGS avoids a
false positive report when using os/user.

Change-Id: I0905c644ff7f003b6718aac782393fa219514c48
Reviewed-on: https://go-review.googlesource.com/23492
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

misc/cgo/testsanitizers/test.bash

@@ -154,6 +154,17 @@ if test "$tsan" = "yes"; then
 	status=1
     fi
 
+    # This test requires rebuilding os/user with -fsanitize=thread.
+    if ! CGO_CFLAGS="-fsanitize=thread" CGO_LDFLAGS="-fsanitize=thread" go run -installsuffix=tsan tsan5.go 2>$err; then
+	cat $err
+	echo "FAIL: tsan5"
+	status=1
+    elif grep -i warning $err >/dev/null 2>&1; then
+	cat $err
+	echo "FAIL: tsan5"
+	status=1
+    fi
+
     rm -f $err
 fi
 

misc/cgo/testsanitizers/tsan5.go

+// 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
+
+// Check that calls to C.malloc/C.free do not collide with the calls
+// made by the os/user package.
+
+// #cgo CFLAGS: -fsanitize=thread
+// #cgo LDFLAGS: -fsanitize=thread
+// #include <stdlib.h>
+import "C"
+
+import (
+	"fmt"
+	"os"
+	"os/user"
+	"runtime"
+	"sync"
+)
+
+func main() {
+	u, err := user.Current()
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		// Let the test pass.
+		os.Exit(0)
+	}
+
+	var wg sync.WaitGroup
+	for i := 0; i < 20; i++ {
+		wg.Add(2)
+		go func() {
+			defer wg.Done()
+			for i := 0; i < 1000; i++ {
+				user.Lookup(u.Username)
+				runtime.Gosched()
+			}
+		}()
+		go func() {
+			defer wg.Done()
+			for i := 0; i < 1000; i++ {
+				p := C.malloc(C.size_t(len(u.Username) + 1))
+				runtime.Gosched()
+				C.free(p)
+			}
+		}()
+	}
+	wg.Wait()
+}

src/cmd/cgo/out.go

@@ -1324,6 +1324,7 @@ const noTsanProlog = `
 #define _cgo_tsan_release()
 `
 
+// This must match the TSAN code in runtime/cgo/libcgo.h.
 const yesTsanProlog = `
 #define CGO_NO_SANITIZE_THREAD __attribute__ ((no_sanitize_thread))
 
@@ -1332,10 +1333,12 @@ long long _cgo_sync __attribute__ ((common));
 extern void __tsan_acquire(void*);
 extern void __tsan_release(void*);
 
+__attribute__ ((unused))
 static void _cgo_tsan_acquire() {
 	__tsan_acquire(&_cgo_sync);
 }
 
+__attribute__ ((unused))
 static void _cgo_tsan_release() {
 	__tsan_release(&_cgo_sync);
 }

src/runtime/cgo/gcc_linux_amd64.c

@@ -89,7 +89,9 @@ threadentry(void *v)
 	ThreadStart ts;
 
 	ts = *(ThreadStart*)v;
+	_cgo_tsan_acquire();
 	free(v);
+	_cgo_tsan_release();
 
 	/*
 	 * Set specific keys.

src/runtime/cgo/gcc_util.c

@@ -11,7 +11,9 @@ x_cgo_thread_start(ThreadStart *arg)
 	ThreadStart *ts;
 
 	/* Make our own copy that can persist after we return. */
+	_cgo_tsan_acquire();
 	ts = malloc(sizeof *ts);
+	_cgo_tsan_release();
 	if(ts == nil) {
 		fprintf(stderr, "runtime/cgo: out of memory in thread_start\n");
 		abort();

src/runtime/cgo/libcgo.h

@@ -94,3 +94,42 @@ struct context_arg {
 	uintptr_t Context;
 };
 extern void (*x_cgo_context_function)(struct context_arg*);
+
+/*
+ * TSAN support.  This is only useful when building with
+ *   CGO_CFLAGS="-fsanitize=thread" CGO_LDFLAGS="-fsanitize=thread" go install
+ */
+#undef CGO_TSAN
+#if defined(__has_feature)
+# if __has_feature(thread_sanitizer)
+#  define CGO_TSAN
+# endif
+#elif defined(__SANITIZE_THREAD__)
+# define CGO_TSAN
+#endif
+
+#ifdef CGO_TSAN
+
+// These must match the definitions in yesTsanProlog in cmd/cgo/out.go.
+
+long long _cgo_sync __attribute__ ((common));
+
+extern void __tsan_acquire(void*);
+extern void __tsan_release(void*);
+
+__attribute__ ((unused))
+static void _cgo_tsan_acquire() {
+	__tsan_acquire(&_cgo_sync);
+}
+
+__attribute__ ((unused))
+static void _cgo_tsan_release() {
+	__tsan_release(&_cgo_sync);
+}
+
+#else // !defined(CGO_TSAN)
+
+#define _cgo_tsan_acquire()
+#define _cgo_tsan_release()
+
+#endif // !defined(CGO_TSAN)