We won't change i_xtime in ldiskfs code path. But also
need keep normal function out of Lustre. So we using
S_NOCMTIME to indicate invoked from Lustre.

Index: linux-3.10.0-123.13.2.el7.x86_64/fs/ext4/ext4.h
===================================================================
--- linux-3.10.0-123.13.2.el7.x86_64.orig/fs/ext4/ext4.h
+++ linux-3.10.0-123.13.2.el7.x86_64/fs/ext4/ext4.h
@@ -1336,6 +1336,8 @@ static inline struct ext4_inode_info *EX
 
 static inline struct timespec ext4_current_time(struct inode *inode)
 {
+	if (IS_NOCMTIME(inode))
+		return inode->i_ctime;
 	return (inode->i_sb->s_time_gran < NSEC_PER_SEC) ?
 		current_fs_time(inode->i_sb) : CURRENT_TIME_SEC;
 }