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

1 files changed, 9 insertions, 1 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index d8a4afc5eedb..cd918823b352 100644
--- 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) {