Re: [PATCH 1/2] ext4: fix DAX write locking

Jan Kara
2017-01-11T09:01:36Z

On Tue 10-01-17 16:48:07, Christoph Hellwig wrote:
> Unlike O_DIRECT DAX is not an optional opt-in feature selected by the
> application, so we'll have to provide the traditional synchronіzation
> of overlapping writes as we do for buffered writes.
>
> This was broken historically for DAX, but got fixed for ext2 and XFS
> as part of the iomap conversion. Fix up ext4 as well.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Makes sense. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

Ted, can you please pick it up? Thanks!

Honza

> ---
> fs/ext4/file.c | 10 +---------
> 1 file changed, 1 insertion(+), 9 deletions(-)
>
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index d663d3d..a1e88aa 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -175,7 +175,6 @@ ext4_dax_write_iter(struct kiocb *iocb, struct iov_iter *from)
> {
> struct inode *inode = file_inode(iocb->ki_filp);
> ssize_t ret;
> - bool overwrite = false;
>
> inode_lock(inode);
> ret = ext4_write_checks(iocb, from);
> @@ -188,16 +187,9 @@ ext4_dax_write_iter(struct kiocb *iocb, struct iov_iter *from)
> if (ret)
> goto out;
>
> - if (ext4_overwrite_io(inode, iocb->ki_pos, iov_iter_count(from))) {
> - overwrite = true;
> - downgrade_write(&inode->i_rwsem);
> - }
> ret = dax_iomap_rw(iocb, from, &ext4_iomap_ops);
> out:
> - if (!overwrite)
> - inode_unlock(inode);
> - else
> - inode_unlock_shared(inode);
> + inode_unlock(inode);
> if (ret > 0)
> ret = generic_write_sync(iocb, ret);
> return ret;
> --
> 2.1.4
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR