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    Subject[patch 57/60] ext4: Fix sub-block zeroing for writes into preallocated extents

    -stable review patch. If anyone has any objections, please let us know.

    ------------------
    From: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

    (cherry picked from commit 9c1ee184a30394e54165fa4c15923cabd952c106)

    We need to mark the buffer_head mapping preallocated space as new
    during write_begin. Otherwise we don't zero out the page cache content
    properly for a partial write. This will cause file corruption with
    preallocation.

    Now that we mark the buffer_head new we also need to have a valid
    buffer_head blocknr so that unmap_underlying_metadata() unmaps the
    correct block.

    Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
    ---
    fs/ext4/extents.c | 2 ++
    fs/ext4/inode.c | 7 +++++++
    2 files changed, 9 insertions(+)

    --- a/fs/ext4/extents.c
    +++ b/fs/ext4/extents.c
    @@ -2670,6 +2670,8 @@ int ext4_ext_get_blocks(handle_t *handle
    if (allocated > max_blocks)
    allocated = max_blocks;
    set_buffer_unwritten(bh_result);
    + bh_result->b_bdev = inode->i_sb->s_bdev;
    + bh_result->b_blocknr = newblock;
    goto out2;
    }

    --- a/fs/ext4/inode.c
    +++ b/fs/ext4/inode.c
    @@ -2131,6 +2131,13 @@ static int ext4_da_get_block_prep(struct
    set_buffer_delay(bh_result);
    } else if (ret > 0) {
    bh_result->b_size = (ret << inode->i_blkbits);
    + /*
    + * With sub-block writes into unwritten extents
    + * we also need to mark the buffer as new so that
    + * the unwritten parts of the buffer gets correctly zeroed.
    + */
    + if (buffer_unwritten(bh_result))
    + set_buffer_new(bh_result);
    ret = 0;
    }




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