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: Lukas Czerner <lczerner@redhat.com>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: "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)