ext4: init pagevec in ext4_da_block_invalidatepages

ext4_da_block_invalidatepages is missing a pagevec_init(),
which means that pvec->cold contains random garbage.

This affects whether the page goes to the front or
back of the LRU when ->cold makes it to
free_hot_cold_page()
Reviewed-by: NLukas Czerner <lczerner@redhat.com>
Reviewed-by: NCarlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: NEric Sandeen <sandeen@redhat.com>
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org

fs/ext4/inode.c

@@ -1482,6 +1482,7 @@ static void ext4_da_block_invalidatepages(struct mpage_da_data *mpd)
 	last = end << (PAGE_CACHE_SHIFT - inode->i_blkbits);
 	ext4_es_remove_extent(inode, start, last - start + 1);
 
+	pagevec_init(&pvec, 0);
 	while (index <= end) {
 		nr_pages = pagevec_lookup(&pvec, mapping, index, PAGEVEC_SIZE);
 		if (nr_pages == 0)