diff --git a/src/cmd/go/internal/fsys/fsys.go b/src/cmd/go/internal/fsys/fsys.go
index d96a290..0d7bef9 100644
--- a/src/cmd/go/internal/fsys/fsys.go
+++ b/src/cmd/go/internal/fsys/fsys.go
@@ -464,28 +464,20 @@
 // walk recursively descends path, calling walkFn. Copied, with some
 // modifications from path/filepath.walk.
 func walk(path string, info fs.FileInfo, walkFn filepath.WalkFunc) error {
-	if !info.IsDir() {
-		return walkFn(path, info, nil)
+	if err := walkFn(path, info, nil); err != nil || !info.IsDir() {
+		return err
 	}
 
-	fis, readErr := ReadDir(path)
-	walkErr := walkFn(path, info, readErr)
-	// If readErr != nil, walk can't walk into this directory.
-	// walkErr != nil means walkFn want walk to skip this directory or stop walking.
-	// Therefore, if one of readErr and walkErr isn't nil, walk will return.
-	if readErr != nil || walkErr != nil {
-		// The caller's behavior is controlled by the return value, which is decided
-		// by walkFn. walkFn may ignore readErr and return nil.
-		// If walkFn returns SkipDir, it will be handled by the caller.
-		// So walk should return whatever walkFn returns.
-		return walkErr
+	fis, err := ReadDir(path)
+	if err != nil {
+		return walkFn(path, info, err)
 	}
 
 	for _, fi := range fis {
 		filename := filepath.Join(path, fi.Name())
-		if walkErr = walk(filename, fi, walkFn); walkErr != nil {
-			if !fi.IsDir() || walkErr != filepath.SkipDir {
-				return walkErr
+		if err := walk(filename, fi, walkFn); err != nil {
+			if !fi.IsDir() || err != filepath.SkipDir {
+				return err
 			}
 		}
 	}
diff --git a/src/cmd/go/testdata/script/fsys_walk.txt b/src/cmd/go/testdata/script/fsys_walk.txt
new file mode 100644
index 0000000..9d1a945
--- /dev/null
+++ b/src/cmd/go/testdata/script/fsys_walk.txt
@@ -0,0 +1,6 @@
+# Test that go list prefix... does not read directories not beginning with prefix.
+env GODEBUG=gofsystrace=1
+go list m...
+stderr mime
+stderr mime[\\/]multipart
+! stderr archive
diff --git a/src/cmd/go/testdata/script/list_permissions.txt b/src/cmd/go/testdata/script/list_perm.txt
similarity index 99%
rename from src/cmd/go/testdata/script/list_permissions.txt
rename to src/cmd/go/testdata/script/list_perm.txt
index f65896c..3b850ef3 100644
--- a/src/cmd/go/testdata/script/list_permissions.txt
+++ b/src/cmd/go/testdata/script/list_perm.txt
@@ -11,12 +11,11 @@
 go list ./empty/...
 stderr 'matched no packages'
 
-[root] stop # Root typically ignores file permissions.
-
 # Make the directory ./noread unreadable, and verify that 'go list' reports an
 # explicit error for a pattern that should match it (rather than treating it as
 # equivalent to an empty directory).
 
+[root] stop # Root typically ignores file permissions.
 [windows] skip # Does not have Unix-style directory permissions.
 [plan9] skip   # Might not have Unix-style directory permissions.
 
diff --git a/src/cmd/go/testdata/script/mod_perm.txt b/src/cmd/go/testdata/script/mod_perm.txt
new file mode 100644
index 0000000..f5382ec
--- /dev/null
+++ b/src/cmd/go/testdata/script/mod_perm.txt
@@ -0,0 +1,23 @@
+# go list should work in ordinary conditions.
+go list ./...
+! stdout _data
+
+# skip in conditions where chmod 0 may not work.
+# plan9 should be fine, but copied from list_perm.txt unchanged.
+[root] skip
+[windows] skip
+[plan9] skip
+
+# go list should work with unreadable _data directory.
+chmod 0 _data
+go list ./...
+! stdout _data
+
+-- go.mod --
+module m
+
+-- x.go --
+package m
+
+-- _data/x.go --
+package p