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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
This commit is contained in:
Jan Kara 2016-09-30 02:02:29 -04:00 committed by Theodore Ts'o
parent 51e8137b82
commit 9b623df614
1 changed files with 9 additions and 1 deletions
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10
fs/ext4/inode.c
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@ -647,11 +647,19 @@ int ext4_map_blocks(handle_t *handle, struct inode *inode,
/*
* 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) {