ext4: Release page references acquired in ext4_da_block_invalidatepages

We forget to release page references we acquire in
ext4_da_block_invalidatepages.  Luckily, this function gets called only if we
are not able to allocate blocks for delay-allocated data so that function
should better never be called.

Also cleanup handling of index variable.
Reported-by: NWu Fengguang <fengguang.wu@intel.com>
Signed-off-by: NJan Kara <jack@suse.cz>
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>

fs/ext4/inode.c

@@ -2157,17 +2157,16 @@ static void ext4_da_block_invalidatepages(struct mpage_da_data *mpd,
 			break;
 		for (i = 0; i < nr_pages; i++) {
 			struct page *page = pvec.pages[i];
-			index = page->index;
-			if (index > end)
+			if (page->index > end)
 				break;
-			index++;
-
 			BUG_ON(!PageLocked(page));
 			BUG_ON(PageWriteback(page));
 			block_invalidatepage(page, 0);
 			ClearPageUptodate(page);
 			unlock_page(page);
 		}
+		index = pvec.pages[nr_pages - 1]->index + 1;
+		pagevec_release(&pvec);
 	}
 	return;
 }