On Mon, Apr 08, 2013 at 06:27:43PM +0200, Jan Kara wrote:
> When ext4 is mounted in dioread_nolock mode, it calls
> __blockdev_direct_IO() without DIO_LOCKING flag which also means mapping
> is not synced before direct IO starts. As a result consistency between
> buffered writes and following direct IO reads is broken. More
> importantly, if the file is truncated, and extented back, zeroing of the
> tail page is not visible to the following direct IO read which will return
> stale data.
>
> Fix the problem by flushing dirty pages before issuing direct IO read.
>
> Signed-off-by: Jan Kara <jack@xxxxxxx>
> ---
> fs/ext4/indirect.c | 4 ++++
> 1 files changed, 4 insertions(+), 0 deletions(-)
>
> diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
> index b505a14..c18bf1c 100644
> --- a/fs/ext4/indirect.c
> +++ b/fs/ext4/indirect.c
> @@ -809,6 +809,10 @@ ssize_t ext4_ind_direct_IO(int rw, struct kiocb *iocb,
>
> retry:
> if (rw == READ && ext4_should_dioread_nolock(inode)) {
> + ret = filemap_write_and_wait_range(inode->i_mapping, offset,
> + offset + count - 1);
> + if (ret)
> + goto out;
> if (unlikely(atomic_read(&EXT4_I(inode)->i_unwritten))) {
> mutex_lock(&inode->i_mutex);
> ext4_flush_unwritten_io(inode);
Hi Jan,
Sorry for the late reply. I have a question about this patch. In your
patch, we flush dirty pages befoer issuing a dio read. But we have
flushed dirty pages in generic_file_aio_read(). So is it really
necessary to flush dirty pages again?
Regards,
- Zheng
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