ext4: unmap metadata when zeroing blocks

When zeroing blocks for DAX allocations, we also have to unmap aliases
in the block device mappings.  Otherwise writeback can overwrite zeros
with stale data from block device page cache.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index d8a4afc5eedbcc6b4cc790ea1f011d469ea5d06a..cd918823b3528c7ffa76992d245047ee1d750235 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -647,11 +647,19 @@ found:
                /*
                 * We have to zeroout blocks before inserting them into extent
                 * status tree. Otherwise someone could look them up there and
-                * use them before they are really zeroed.
+                * use them before they are really zeroed. We also have to
+                * unmap metadata before zeroing as otherwise writeback can
+                * overwrite zeros with stale data from block device.
                 */
                if (flags & EXT4_GET_BLOCKS_ZERO &&
                    map->m_flags & EXT4_MAP_MAPPED &&
                    map->m_flags & EXT4_MAP_NEW) {
+                       ext4_lblk_t i;
+
+                       for (i = 0; i < map->m_len; i++) {
+                               unmap_underlying_metadata(inode->i_sb->s_bdev,
+                                                         map->m_pblk + i);
+                       }
                        ret = ext4_issue_zeroout(inode, map->m_lblk,
                                                 map->m_pblk, map->m_len);
                        if (ret) {