Fix time.Since() in defer. Wrap in anonymous function (#11489)

Function arguments in defer evaluated during definition of defer, not
during execution

Signed-off-by: Slavik Panasovets <slavik@google.com>

Signed-off-by: Slavik Panasovets <slavik@google.com>

discovery/refresh/refresh.go

@@ -114,7 +114,10 @@ func (d *Discovery) Run(ctx context.Context, ch chan<- []*targetgroup.Group) {
 
 func (d *Discovery) refresh(ctx context.Context) ([]*targetgroup.Group, error) {
 	now := time.Now()
-	defer d.duration.Observe(time.Since(now).Seconds())
+	defer func() {
+		d.duration.Observe(time.Since(now).Seconds())
+	}()
+
 	tgs, err := d.refreshf(ctx)
 	if err != nil {
 		d.failures.Inc()

tsdb/db.go

@@ -1939,7 +1939,9 @@ func (db *DB) CleanTombstones() (err error) {
 	defer db.cmtx.Unlock()
 
 	start := time.Now()
-	defer db.metrics.tombCleanTimer.Observe(time.Since(start).Seconds())
+	defer func() {
+		db.metrics.tombCleanTimer.Observe(time.Since(start).Seconds())
+	}()
 
 	cleanUpCompleted := false
 	// Repeat cleanup until there is no tombstones left.