GFS2: Get a block reservation before resizing a file

This patch allocates a block reservation structure before growing
or shrinking a file. Without this structure, the grow or shink code
can reference the bad pointer.
Signed-off-by: NBob Peterson <rpeterso@redhat.com>
Signed-off-by: NSteven Whitehouse <swhiteho@redhat.com>

fs/gfs2/bmap.c

@@ -1288,6 +1288,10 @@ int gfs2_setattr_size(struct inode *inode, u64 newsize)
 
 	inode_dio_wait(inode);
 
+	ret = gfs2_rs_alloc(GFS2_I(inode));
+	if (ret)
+		return ret;
+
 	oldsize = inode->i_size;
 	if (newsize >= oldsize)
 		return do_grow(inode, newsize);