From 5195460c95a1162bae565968661644533e8a07ce Mon Sep 17 00:00:00 2001
From: Julius Volz <julius.volz@gmail.com>
Date: Mon, 13 Sep 2021 16:12:48 +0200
Subject: [PATCH] Correctly call default silence maintenance function (#2701)

https://github.com/prometheus/alertmanager/pull/2689 introduced a
regression where the default maintenance function would no longer be
called even if no override was specified. The Alertmanager now crashes
on any silence maintenance run without this fix.

Signed-off-by: Julius Volz <julius.volz@gmail.com>
---
 silence/silence.go      |  2 +-
 silence/silence_test.go | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/silence/silence.go b/silence/silence.go
index c61dac50..11adc9bc 100644
--- a/silence/silence.go
+++ b/silence/silence.go
@@ -378,7 +378,7 @@ func (s *Silences) Maintenance(interval time.Duration, snapf string, stopc <-cha
 		return size, f.Close()
 	}
 
-	if doMaintenance != nil {
+	if override != nil {
 		doMaintenance = override
 	}
 
diff --git a/silence/silence_test.go b/silence/silence_test.go
index 1e86a9b8..3674da27 100644
--- a/silence/silence_test.go
+++ b/silence/silence_test.go
@@ -180,6 +180,25 @@ func TestSilencesSnapshot(t *testing.T) {
 	}
 }
 
+// This tests a regression introduced by https://github.com/prometheus/alertmanager/pull/2689.
+func TestSilences_Maintenance_DefaultMaintenanceFuncDoesntCrash(t *testing.T) {
+	f, err := ioutil.TempFile("", "snapshot")
+	require.NoError(t, err, "creating temp file failed")
+	s := &Silences{st: state{}, logger: log.NewNopLogger(), now: utcNow, metrics: newMetrics(nil, nil)}
+	stopc := make(chan struct{})
+
+	done := make(chan struct{})
+	go func() {
+		s.Maintenance(100*time.Millisecond, f.Name(), stopc, nil)
+		close(done)
+	}()
+
+	time.Sleep(200 * time.Millisecond)
+	close(stopc)
+
+	<-done
+}
+
 func TestSilences_Maintenance_SupportsCustomCallback(t *testing.T) {
 	f, err := ioutil.TempFile("", "snapshot")
 	require.NoError(t, err, "creating temp file failed")