Merge pull request #1683 from qieqieplus/master

fix race condition when loading volumes concurrently

weed/storage/disk_location.go

@@ -99,12 +99,14 @@ func (l *DiskLocation) loadExistingVolume(fileInfo os.FileInfo, needleMapKind Ne
 	}
 
 	// avoid loading one volume more than once
-	l.volumesLock.RLock()
-	_, found := l.volumes[vid]
-	l.volumesLock.RUnlock()
-	if found {
+	l.volumesLock.Lock()
+	if _, found := l.volumes[vid]; found {
+		l.volumesLock.Unlock()
 		glog.V(1).Infof("loaded volume, %v", vid)
 		return true
+	} else {
+		l.volumes[vid] = nil
+		l.volumesLock.Unlock()
 	}
 
 	// load the volume