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ext4: implement allocation of pre-zeroed blocks

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DAX page fault path needs to get blocks that are pre-zeroed to avoid
races when two concurrent page faults happen in the same block of a
file. Implement support for this in ext4_map_blocks().

Signed-off-by: Jan Kara <jack@suse.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Jan Kara
2015-12-07 15:10:26 -05:00
committed by Theodore Ts'o
parent 53085fac02
commit c86d8db33a
4 changed files with 36 additions and 4 deletions
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25
fs/ext4/inode.c
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@@ -636,6 +636,22 @@ found:
WARN_ON(1);
}
/*
* 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.
*/
if (flags & EXT4_GET_BLOCKS_ZERO &&
map->m_flags & EXT4_MAP_MAPPED &&
map->m_flags & EXT4_MAP_NEW) {
ret = ext4_issue_zeroout(inode, map->m_lblk,
map->m_pblk, map->m_len);
if (ret) {
retval = ret;
goto out_sem;
}
}
/*
* If the extent has been zeroed out, we don't need to update
* extent status tree.
@@ -643,7 +659,7 @@ found:
if ((flags & EXT4_GET_BLOCKS_PRE_IO) &&
ext4_es_lookup_extent(inode, map->m_lblk, &es)) {
if (ext4_es_is_written(&es))
goto has_zeroout;
goto out_sem;
}
status = map->m_flags & EXT4_MAP_UNWRITTEN ?
EXTENT_STATUS_UNWRITTEN : EXTENT_STATUS_WRITTEN;
@@ -654,11 +670,13 @@ found:
status |= EXTENT_STATUS_DELAYED;
ret = ext4_es_insert_extent(inode, map->m_lblk, map->m_len,
map->m_pblk, status);
if (ret < 0)
if (ret < 0) {
retval = ret;
goto out_sem;
}
}
has_zeroout:
out_sem:
up_write((&EXT4_I(inode)->i_data_sem));
if (retval > 0 && map->m_flags & EXT4_MAP_MAPPED) {
ret = check_block_validity(inode, map);
@@ -3083,6 +3101,7 @@ int ext4_get_block_dax(struct inode *inode, sector_t iblock,
struct buffer_head *bh_result, int create)
{
int flags = EXT4_GET_BLOCKS_PRE_IO | EXT4_GET_BLOCKS_UNWRIT_EXT;
if (create)
flags |= EXT4_GET_BLOCKS_CREATE;
ext4_debug("ext4_get_block_dax: inode %lu, create flag %d\n",