Re: [PATCH] ovl: disable IOCB_DIO_CALLER_COMP

Zorro Lang
2023-09-26T15:24:21Z

On Mon, Sep 25, 2023 at 12:21:35AM -0600, Jens Axboe wrote:
> overlayfs copies the kiocb flags when it sets up a new kiocb to handle
> a write, but it doesn't properly support dealing with the deferred
> caller completions of the kiocb. This means it doesn't get the final
> write completion value, and hence will complete the write with '0' as
> the result.
>
> We could support the caller completions in overlayfs, but for now let's
> just disable them in the generated write kiocb.
>
> Reported-by: Zorro Lang <zlang@redhat.com>
> Link: https://lore.kernel.org/io-uring/20230924142754.ejwsjen5pvyc32l4@dell-per750-06-vm-08.rhts.eng.pek2.redhat.com/
> Fixes: 8c052fb3002e ("iomap: support IOCB_DIO_CALLER_COMP")
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>
> ---

Thanks Jens, the fstests generic/617 works on latest linux kernel with this
patch now.

>
> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> index 4193633c4c7a..693971d20280 100644
> --- a/fs/overlayfs/file.c
> +++ b/fs/overlayfs/file.c
> @@ -391,6 +391,12 @@ static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter)
> if (!ovl_should_sync(OVL_FS(inode->i_sb)))
> ifl &= ~(IOCB_DSYNC | IOCB_SYNC);
>
> + /*
> + * Overlayfs doesn't support deferred completions, don't copy
> + * this property in case it is set by the issuer.
> + */
> + ifl &= ~IOCB_DIO_CALLER_COMP;
> +
> old_cred = ovl_override_creds(file_inode(file)->i_sb);
> if (is_sync_kiocb(iocb)) {
> file_start_write(real.file);
>
> --
> Jens Axboe
>
>
>