On Mon, Jan 13, 2020 at 04:34:21PM +0530, Ritesh Harjani wrote:
> Some filesystems (e.g. ext4) need to know in it's writeback path, that
> whether DIO is in progress or not. This info may be needed to avoid the
> stale data exposure race with DIO reads.
Does XFS have this problem too?
Admittedly dio read during mmap write is probably not well supported. ;)
> Signed-off-by: Ritesh Harjani <riteshh@xxxxxxxxxxxxx>
> ---
> fs/iomap/direct-io.c | 17 +++++++++++++----
Might want to cc fsdevel and the iomap maintainers...
--D
> 1 file changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index 23837926c0c5..d1c159bd3854 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -468,9 +468,18 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
> flags |= IOMAP_NOWAIT;
> }
>
> + /*
> + * Call inode_dio_begin() before we write out and wait for writeback to
> + * complete. This may be needed by some filesystems to prevent race
> + * like stale data exposure by DIO reads.
> + */
> + inode_dio_begin(inode);
> + /* So that i_dio_count is incremented before below operation */
> + smp_mb__after_atomic();
> +
> ret = filemap_write_and_wait_range(mapping, pos, end);
> if (ret)
> - goto out_free_dio;
> + goto out_end_dio;
>
> /*
> * Try to invalidate cache pages for the range we're direct
> @@ -488,11 +497,9 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
> !inode->i_sb->s_dio_done_wq) {
> ret = sb_init_dio_done_wq(inode->i_sb);
> if (ret < 0)
> - goto out_free_dio;
> + goto out_end_dio;
> }
>
> - inode_dio_begin(inode);
> -
> blk_start_plug(&plug);
> do {
> ret = iomap_apply(inode, pos, count, flags, ops, dio,
> @@ -568,6 +575,8 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
>
> return iomap_dio_complete(dio);
>
> +out_end_dio:
> + inode_dio_end(inode);
> out_free_dio:
> kfree(dio);
> return ret;
> --
> 2.21.0
>
