linux-kernel - Re: [PATCH] ovl: disable IOCB_DIO_CALLER

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Date:   Tue, 26 Sep 2023 23:23:28 +0800
From:   Zorro Lang <zlang@...hat.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Amir Goldstein <amir73il@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-unionfs@...r.kernel.org
Subject: Re: [PATCH] ovl: disable IOCB_DIO_CALLER_COMP

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@...hat.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@...nel.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
> 
> 	
>