syscall: skip TestUseCgroupFD if cgroupfs mounted RO

The skipping logic should also trigger if /sys/fs/cgroup is
mounted read-only too. This is how it is mounted on the
ppc64le/p10 containers today.

Fixes #57262

Change-Id: Idc0ab050052ebf5777ac09f9519215b437b0ee7c
Reviewed-on: https://go-review.googlesource.com/c/go/+/456835
Reviewed-by: Ian Lance Taylor <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>
Auto-Submit: Bryan Mills <[email protected]>
Run-TryBot: Paul Murphy <[email protected]>

Author: pmur

src/syscall/exec_linux_test.go

@@ -8,6 +8,7 @@ package syscall_test
 
 import (
 	"bytes"
+	"errors"
 	"flag"
 	"fmt"
 	"internal/testenv"
@@ -504,7 +505,8 @@ func prepareCgroupFD(t *testing.T) (int, string) {
 	// Need an ability to create a sub-cgroup.
 	subCgroup, err := os.MkdirTemp(prefix+string(bytes.TrimSpace(cg)), "subcg-")
 	if err != nil {
-		if os.IsPermission(err) {
+		// Running in an unprivileged container, this may also return EROFS #57262.
+		if os.IsPermission(err) || errors.Is(err, syscall.EROFS) {
 			t.Skip(err)
 		}
 		t.Fatal(err)