NFSD: Fix bad update of layout in nfsd4_return_file_layout

With return layout as, (seg is return layout, lo is record layout)
seg->offset <= lo->offset and layout_end(seg) < layout_end(lo),
nfsd should update lo's offset to seg's end,
and,
seg->offset > lo->offset and layout_end(seg) >= layout_end(lo),
nfsd should update lo's end to seg's offset.

Fixes: 9cf514cc ("nfsd: implement pNFS operations")
Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4layouts.c

@@ -440,15 +440,14 @@ nfsd4_return_file_layout(struct nfs4_layout *lp, struct nfsd4_layout_seg *seg,
 			list_move_tail(&lp->lo_perstate, reaplist);
 			return;
 		}
-		end = seg->offset;
+		lo->offset = layout_end(seg);
 	} else {
 		/* retain the whole layout segment on a split. */
 		if (layout_end(seg) < end) {
 			dprintk("%s: split not supported\n", __func__);
 			return;
 		}
-
-		lo->offset = layout_end(seg);
+		end = seg->offset;
 	}
 
 	layout_update_len(lo, end);