On Sun, Sep 09, 2012 at 09:27:14PM +0400, Dmitry Monakhov wrote:
> Jan Kara have spotted interesting issue:
> There are potential data corruption issue with direct IO overwrites
> racing with truncate:
> Like:
> dio write truncate_task
> ->ext4_ext_direct_IO
> ->overwrite == 1
> ->down_read(&EXT4_I(inode)->i_data_sem);
> ->mutex_unlock(&inode->i_mutex);
> ->ext4_setattr()
> ->inode_dio_wait()
> ->truncate_setsize()
> ->ext4_truncate()
> ->down_write(&EXT4_I(inode)->i_data_sem);
> ->__blockdev_direct_IO
> ->ext4_get_block
> ->submit_io()
> ->up_read(&EXT4_I(inode)->i_data_sem);
> # truncate data blocks, allocate them to
> # other inode - bad stuff happens because
> # dio is still in flight.
>
> In order to serialize with truncate dio worker should grab extra i_dio_count
> reference before drop i_mutex.
>
> Changes agains V1:
> - wake up dio waiters before i_mutex.
>
> Reviewed-by: Jan Kara <jack@xxxxxxx>
> Signed-off-by: Dmitry Monakhov <dmonakhov@xxxxxxxxxx>
Hi Dmitry,
Indeed there is a data corruption. This patch looks good to me. You
can add:
Reviewed-by: Zheng Liu <wenqing.lz@xxxxxxxxxx>
Regards,
Zheng
> ---
> fs/ext4/inode.c | 2 ++
> 1 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index a850026..c5c4f9d 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3014,6 +3014,7 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
> overwrite = *((int *)iocb->private);
>
> if (overwrite) {
> + atomic_inc(&inode->i_dio_count);
> down_read(&EXT4_I(inode)->i_data_sem);
> mutex_unlock(&inode->i_mutex);
> }
> @@ -3111,6 +3112,7 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
> retake_lock:
> /* take i_mutex locking again if we do a ovewrite dio */
> if (overwrite) {
> + inode_dio_done(inode);
> up_read(&EXT4_I(inode)->i_data_sem);
> mutex_lock(&inode->i_mutex);
> }
> --
> 1.7.7.6
>
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