runtime: skip TestLockOSThreadAvoidsStatePropagation if one can't unshare

This change splits a testprog out of TestLockOSThreadExit and makes it
its own test. Then, this change makes the testprog exit prematurely with
a special message if unshare fails with EPERM because not all of the
builders allow the user to call the unshare syscall.

Also, do some minor cleanup on the TestLockOSThread* tests.

Fixes #29366.

Change-Id: Id8a9f6c4b16e26af92ed2916b90b0249ba226dbe
Reviewed-on: https://go-review.googlesource.com/c/155437
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

1 files changed, 59 insertions, 0 deletions

diff --git a/src/runtime/testdata/testprog/syscalls_linux.go b/src/runtime/testdata/testprog/syscalls_linux.go
new file mode 100644
index 0000000000..b8ac087626
--- /dev/null
+++ b/src/runtime/testdata/testprog/syscalls_linux.go
@@ -0,0 +1,59 @@
+// Copyright 2017 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
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"syscall"
+)
+
+func gettid() int {
+	return syscall.Gettid()
+}
+
+func tidExists(tid int) (exists, supported bool) {
+	stat, err := ioutil.ReadFile(fmt.Sprintf("/proc/self/task/%d/stat", tid))
+	if os.IsNotExist(err) {
+		return false, true
+	}
+	// Check if it's a zombie thread.
+	state := bytes.Fields(stat)[2]
+	return !(len(state) == 1 && state[0] == 'Z'), true
+}
+
+func getcwd() (string, error) {
+	if !syscall.ImplementsGetwd {
+		return "", nil
+	}
+	// Use the syscall to get the current working directory.
+	// This is imperative for checking for OS thread state
+	// after an unshare since os.Getwd might just check the
+	// environment, or use some other mechanism.
+	var buf [4096]byte
+	n, err := syscall.Getcwd(buf[:])
+	if err != nil {
+		return "", err
+	}
+	// Subtract one for null terminator.
+	return string(buf[:n-1]), nil
+}
+
+func unshareFs() error {
+	err := syscall.Unshare(syscall.CLONE_FS)
+	if err != nil {
+		errno, ok := err.(syscall.Errno)
+		if ok && errno == syscall.EPERM {
+			return errNotPermitted
+		}
+	}
+	return err
+}
+
+func chdir(path string) error {
+	return syscall.Chdir(path)
+}