[XFS] Fix vmtruncate abuse in the XFS setattr ATTR_SIZE operation.

SGI Modid: xfs-linux:xfs-kern:170344a

fs/xfs/linux/xfs_linux.h

@@ -247,10 +247,11 @@ static inline void set_buffer_unwritten_io(struct buffer_head *bh)
 #define howmany(x, y)	(((x)+((y)-1))/(y))
 #define roundup(x, y)	((((x)+((y)-1))/(y))*(y))
 
-static inline void xfs_stack_trace(void)
-{
-	dump_stack();
-}
+#define xfs_stack_trace()	dump_stack()
+
+#define xfs_itruncate_data(ip, off)	\
+	(-vmtruncate(LINVFS_GET_IP(XFS_ITOV(ip)), (off)))
+
 
 /* Move the kernel do_div definition off to one side */
 

fs/xfs/xfs_vnodeops.c

@@ -680,18 +680,12 @@ xfs_setattr(
 	 * once it is a part of the transaction.
 	 */
 	if (mask & XFS_AT_SIZE) {
-		if (vap->va_size > ip->i_d.di_size) {
-			code = xfs_igrow_start(ip, vap->va_size, credp);
-			xfs_iunlock(ip, XFS_ILOCK_EXCL);
-		} else if (vap->va_size <= ip->i_d.di_size) {
-			xfs_iunlock(ip, XFS_ILOCK_EXCL);
-			xfs_itruncate_start(ip, XFS_ITRUNC_DEFINITE,
-					    (xfs_fsize_t)vap->va_size);
 		code = 0;
-		} else {
+		if (vap->va_size > ip->i_d.di_size)
+			code = xfs_igrow_start(ip, vap->va_size, credp);
 		xfs_iunlock(ip, XFS_ILOCK_EXCL);
-			code = 0;
-		}
+		if (!code)
+			code = xfs_itruncate_data(ip, vap->va_size);
 		if (code) {
 			ASSERT(tp == NULL);
 			lock_flags &= ~XFS_ILOCK_EXCL;