fix: prevent SIGTERM/reload deadlock (#7562)

plugin/reload/reload.go

@@ -105,6 +105,10 @@ func hook(event caddy.EventName, info any) error {
 					// now lets consider that plugin will not be reload, unless appear in next config file
 					// change status of usage will be reset in setup if the plugin appears in config file
 					r.setUsage(maybeUsed)
+					// If shutdown is in progress, avoid attempting a restart.
+					if shutdownRequested(r.quit) {
+						return
+					}
 					_, err := instance.Restart(corefile)
 					reloadInfo.WithLabelValues("sha512", hex.EncodeToString(sha512sum[:])).Set(1)
 					if err != nil {
@@ -126,3 +130,14 @@ func hook(event caddy.EventName, info any) error {
 
 	return nil
 }
+
+// shutdownRequested reports whether a shutdown has been requested via quit channel.
+// helps with unit testing of the shutdown gate logic.
+func shutdownRequested(quit <-chan bool) bool {
+	select {
+	case <-quit:
+		return true
+	default:
+		return false
+	}
+}

plugin/reload/reload_test.go

@@ -0,0 +1,50 @@
+package reload
+
+import (
+	"testing"
+
+	"github.com/coredns/caddy"
+)
+
+// fakeInput implements caddy.Input for testing parse().
+type fakeInput struct {
+	p string
+	b []byte
+}
+
+func (f fakeInput) ServerType() string { return "dns" }
+func (f fakeInput) Body() []byte       { return f.b }
+func (f fakeInput) Path() string       { return f.p }
+
+// TestParseInvalidCorefile ensures parse returns an error for invalid Corefile syntax.
+func TestParseInvalidCorefile(t *testing.T) {
+	t.Parallel()
+
+	broken := fakeInput{p: "Corefile", b: []byte(". { errors\n")}
+	if _, err := parse(broken); err == nil {
+		t.Fatalf("expected parse error for invalid Corefile, got nil")
+	}
+}
+
+// TestShutdownGate ensures the shutdown gate helper recognizes when shutdown is requested.
+func TestShutdownGate(t *testing.T) {
+	t.Parallel()
+
+	q := make(chan bool, 1)
+	if shutdownRequested(q) {
+		t.Fatalf("expected no shutdown before signal")
+	}
+	q <- true
+	if !shutdownRequested(q) {
+		t.Fatalf("expected shutdown after signal")
+	}
+}
+
+// TestHookIgnoresNonStartupEvent ensures hook is a no-op for non-startup events.
+func TestHookIgnoresNonStartupEvent(t *testing.T) {
+	t.Parallel()
+
+	if err := hook(caddy.EventName("not-startup"), nil); err != nil {
+		t.Fatalf("expected no error for non-startup event, got %v", err)
+	}
+}

plugin/reload/setup.go

@@ -20,7 +20,7 @@ func init() { plugin.Register("reload", setup) }
 // channel for QUIT is never changed in purpose.
 // WARNING: this data may be unsync after an invalid attempt of reload Corefile.
 var (
-	r              = reload{dur: defaultInterval, u: unused, quit: make(chan bool)}
+	r              = reload{dur: defaultInterval, u: unused, quit: make(chan bool, 1)}
 	once, shutOnce sync.Once
 )