avoid concurrent access to map object

fix https://github.com/chrislusf/seaweedfs/issues/2866

weed/mount/page_writer/page_chunk_swapfile.go

@@ -5,6 +5,7 @@ import (
 	"github.com/chrislusf/seaweedfs/weed/util"
 	"github.com/chrislusf/seaweedfs/weed/util/mem"
 	"os"
+	"sync"
 )
 
 var (
@@ -17,6 +18,7 @@ type SwapFile struct {
 	dir                         string
 	file                        *os.File
 	logicToActualChunkIndex     map[LogicChunkIndex]ActualChunkIndex
+	logicToActualChunkIndexLock sync.Mutex
 	chunkSize                   int64
 	freeActualChunkList         []ActualChunkIndex
 }
@@ -52,6 +54,8 @@ func (sf *SwapFile) NewTempFileChunk(logicChunkIndex LogicChunkIndex) (tc *SwapF
 			return nil
 		}
 	}
+	sf.logicToActualChunkIndexLock.Lock()
+	defer sf.logicToActualChunkIndexLock.Unlock()
 	actualChunkIndex, found := sf.logicToActualChunkIndex[logicChunkIndex]
 	if !found {
 		if len(sf.freeActualChunkList) > 0 {
@@ -72,6 +76,9 @@ func (sf *SwapFile) NewTempFileChunk(logicChunkIndex LogicChunkIndex) (tc *SwapF
 }
 
 func (sc *SwapFileChunk) FreeResource() {
+	sc.swapfile.logicToActualChunkIndexLock.Lock()
+	defer sc.swapfile.logicToActualChunkIndexLock.Unlock()
+
 	sc.swapfile.freeActualChunkList = append(sc.swapfile.freeActualChunkList, sc.actualChunkIndex)
 	delete(sc.swapfile.logicToActualChunkIndex, sc.logicChunkIndex)
 }