There will cause a deadlock if invoke ext4_truncate with i_mutex locked
in lustre. Since lustre has own lock to provide protect so we don't
need this check at all. 

Index: linux-3.10.0-123.13.2.el7.x86_64/fs/ext4/inode.c
===================================================================
--- linux-3.10.0-123.13.2.el7.x86_64.orig/fs/ext4/inode.c
+++ linux-3.10.0-123.13.2.el7.x86_64/fs/ext4/inode.c
@@ -3847,8 +3847,6 @@ void ext4_truncate(struct inode *inode)
 	 * or it completely new indode. In those cases we might not
 	 * have i_mutex locked because it's not necessary.
 	 */
-	if (!(inode->i_state & (I_NEW|I_FREEING)))
-		WARN_ON(!mutex_is_locked(&inode->i_mutex));
 	trace_ext4_truncate_enter(inode);
 
 	if (!ext4_can_truncate(inode))