--- ./source/private_module/vol/vol_io/vol_snap_io.c	2018-04-03 02:27:46.000000000 +0000
+++ ./source/private_module/vol/vol_io/vol_snap_io.c.hotpatch	2018-12-14 08:08:46.000000000 +0000
@@ -561,19 +561,19 @@
                ҴСᳬһsglʾҳСÿgrainֻЯһ
                sglΪֻͷŵǰgrainsglnextsglÿգҵǰgrainsgl
                chainϵҳǵsglҳ */
-            curSgl->nextSgl = NULL;
-            curSgl->entrySumInChain = curSgl->entrySumInSgl;
+
+            if (VOL_COW_WRITE == curGrain->grainStep)
+            {
+                curSgl->nextSgl = NULL;
+                curSgl->entrySumInChain = curSgl->entrySumInSgl;
+            }
 
             FREE_PAGES_AND_SGL(volId, volId, curSgl, usageType);
             curGrain->sgl = NULL;
-            //curGrain->extentId = INVALID_EXTENT_ID;
-            //curGrain->offset = INVALID_VALUE32;
         }
     }
-
     return;
 }
-
 /**************************************************************************
      :  дǰУͷgrainÿgrainsglԴ
  :  snapGrain: cow grainϢ
@@ -9181,3 +9181,4 @@
 EXPORT_SYMBOL(getSnapEntryIntfWithEndByVolumeIntf);
 
 EXPORT_SYMBOL(getSnapEntryIntfWithNumByVolumeIntf);
+
