util: fix race in cidr startup

Previously if the `server.cidr_mapping_url` was set and a node
restarted, there was a race condition where `SetOnChange` for the
setting could be called before the `Start` was called. This could result
in it blocking while attempting to submit to the channel.

Fixes: #130589

Release note: None

pkg/util/cidr/cidr.go

@@ -76,22 +76,28 @@ func NewLookup(st *settings.Values) *Lookup {
 	byLength := make([]map[string]string, 0)
 	c.byLength.Store(&byLength)
 	c.lastUpdate.Store(time.Time{})
-	c.changed = make(chan time.Duration)
+	c.changed = make(chan time.Duration, 1)
 
 	cidrMappingUrl.SetOnChange(st, func(ctx context.Context) {
 		log.Infof(ctx, "url changed to '%s'", cidrMappingUrl.Get(st))
 		// Reset the lastUpdate time so that the URL is always reloaded even if
 		// the new file/URL has an older timestamp.
 		c.lastUpdate.Store(time.Time{})
-		c.changed <- cidrRefreshInterval.Get(c.st)
+		select {
+		case c.changed <- cidrRefreshInterval.Get(c.st):
+		default:
+		}
 	})
 	// We have to register this callback first. Otherwise we may run into
 	// an unlikely but possible scenario where we've started the ticker,
 	// and the setting is changed before we register the callback and the
 	// ticker will not be reset to the new value.
 	cidrRefreshInterval.SetOnChange(c.st, func(ctx context.Context) {
 		log.Infof(ctx, "refresh interval changed to '%s'", cidrRefreshInterval.Get(c.st))
-		c.changed <- cidrRefreshInterval.Get(c.st)
+		select {
+		case c.changed <- cidrRefreshInterval.Get(c.st):
+		default:
+		}
 	})
 	return c
 }