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>

diff --git a/misc/cgo/testsanitizers/test.bash b/misc/cgo/testsanitizers/test.bash
index c30df3b6c2a5ec72f4f3dd17436e7bb94b8528cc..1a2a9a697d8f7dd288add6572a9b588549de5bed 100755 (executable)
--- a/misc/cgo/testsanitizers/test.bash
+++ b/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
 

diff --git a/misc/cgo/testsanitizers/tsan5.go b/misc/cgo/testsanitizers/tsan5.go
new file mode 100644 (file)
index 0000000..1214a77
--- /dev/null
+++ b/misc/cgo/testsanitizers/tsan5.go
@@ -0,0 +1,51 @@
+// 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()
+}

diff --git a/src/cmd/cgo/out.go b/src/cmd/cgo/out.go
index 5d6930d3ea402ca09fd9afdefa7f7ebd4d479626..13ee0c4ca70639da5667c7d8a425443bc4d92e34 100644 (file)
--- a/src/cmd/cgo/out.go
+++ b/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);
 }

diff --git a/src/runtime/cgo/gcc_linux_amd64.c b/src/runtime/cgo/gcc_linux_amd64.c
index 50a7e6e078e52a9c6adce5017ae33ce838c94597..0c34c66592aaf15c71775dafe1a8d2d67ec86652 100644 (file)
--- a/src/runtime/cgo/gcc_linux_amd64.c
+++ b/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.

diff --git a/src/runtime/cgo/gcc_util.c b/src/runtime/cgo/gcc_util.c
index 4111fe11951df885c29052c6e2a4b634b842bd13..99af0213314051cc8c9c2ab27fab1dc290ac738e 100644 (file)
--- a/src/runtime/cgo/gcc_util.c
+++ b/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();

diff --git a/src/runtime/cgo/libcgo.h b/src/runtime/cgo/libcgo.h
index 6a484ad4a0c4e21a8460d04996ef5592defd71c7..249d052edc142e611356d506512587b0e9678710 100644 (file)
--- a/src/runtime/cgo/libcgo.h
+++ b/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)