ext4: unmap metadata when zeroing blocks

commit 9b623df614576680cadeaa4d7e0b5884de8f7c17 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index fd5b5e8ba9d4fa57790c655f186302dfb4965bab..f4cdc647ecfc8703490f5b48735a76ee14519e25 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) {