log possible racing condition

fix https://github.com/seaweedfs/seaweedfs/issues/5412

weed/mount/page_writer/page_chunk_mem.go

@@ -63,11 +63,11 @@ func (mc *MemChunk) ReadDataAt(p []byte, off int64, tsNs int64) (maxStop int64)
 		logicStart := max(off, memChunkBaseOffset+t.StartOffset)
 		logicStop := min(off+int64(len(p)), memChunkBaseOffset+t.stopOffset)
 		if logicStart < logicStop {
+			copy(p[logicStart-off:logicStop-off], mc.buf[logicStart-memChunkBaseOffset:logicStop-memChunkBaseOffset])
+			maxStop = max(maxStop, logicStop)
+
 			if t.TsNs >= tsNs {
-				copy(p[logicStart-off:logicStop-off], mc.buf[logicStart-memChunkBaseOffset:logicStop-memChunkBaseOffset])
-				maxStop = max(maxStop, logicStop)
-			} else {
-				println("read old data1", tsNs-t.TsNs, "ns")
+				println("read new data1", t.TsNs - tsNs, "ns")
 			}
 		}
 	}

weed/mount/page_writer/page_chunk_swapfile.go

@@ -129,15 +129,15 @@ func (sc *SwapFileChunk) ReadDataAt(p []byte, off int64, tsNs int64) (maxStop in
 		logicStart := max(off, chunkStartOffset+t.StartOffset)
 		logicStop := min(off+int64(len(p)), chunkStartOffset+t.stopOffset)
 		if logicStart < logicStop {
+			actualStart := logicStart - chunkStartOffset + int64(sc.actualChunkIndex)*sc.swapfile.chunkSize
+			if _, err := sc.swapfile.file.ReadAt(p[logicStart-off:logicStop-off], actualStart); err != nil {
+				glog.Errorf("failed to reading swap file %s: %v", sc.swapfile.file.Name(), err)
+				break
+			}
+			maxStop = max(maxStop, logicStop)
+
 			if t.TsNs >= tsNs {
-				actualStart := logicStart - chunkStartOffset + int64(sc.actualChunkIndex)*sc.swapfile.chunkSize
-				if _, err := sc.swapfile.file.ReadAt(p[logicStart-off:logicStop-off], actualStart); err != nil {
-					glog.Errorf("failed to reading swap file %s: %v", sc.swapfile.file.Name(), err)
-					break
-				}
-				maxStop = max(maxStop, logicStop)
-			} else {
-				println("read old data2", tsNs-t.TsNs, "ns")
+				println("read new data2", t.TsNs - tsNs, "ns")
 			}
 		}
 	}