pkg/subsystem: fix a bug in ReachableParents

Add a test to verify that the function works as intended.

2 files changed, 27 insertions, 5 deletions

diff --git a/pkg/subsystem/entities.go b/pkg/subsystem/entities.go
index b74217bcd..05032e6c2 100644
--- a/pkg/subsystem/entities.go
+++ b/pkg/subsystem/entities.go
@@ -17,15 +17,14 @@ func (subsystem *Subsystem) ReachableParents() map[*Subsystem]struct{} {
 	ret := make(map[*Subsystem]struct{})
 	var dfs func(node *Subsystem)
 	dfs = func(node *Subsystem) {
-		if _, visited := ret[node]; visited {
-			return
-		}
 		for _, p := range node.Parents {
 			if p == subsystem {
 				panic("loop in the parents relation")
 			}
-			ret[p] = struct{}{}
-			dfs(p)
+			if _, visited := ret[p]; !visited {
+				ret[p] = struct{}{}
+				dfs(p)
+			}
 		}
 	}
 	dfs(subsystem)
diff --git a/pkg/subsystem/entities_test.go b/pkg/subsystem/entities_test.go
new file mode 100644
index 000000000..df65dbd5a
--- /dev/null
+++ b/pkg/subsystem/entities_test.go
@@ -0,0 +1,23 @@
+// Copyright 2023 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+package subsystem
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestReachableParents(t *testing.T) {
+	parentParent := &Subsystem{}
+	parentA := &Subsystem{Parents: []*Subsystem{parentParent}}
+	parentB := &Subsystem{Parents: []*Subsystem{parentParent}}
+	entity := &Subsystem{Parents: []*Subsystem{parentA, parentB}}
+
+	retParents := []*Subsystem{}
+	for item := range entity.ReachableParents() {
+		retParents = append(retParents, item)
+	}
+	assert.ElementsMatch(t, retParents, []*Subsystem{parentA, parentB, parentParent})
+}