linux-ext4 - Re: [PATCH RFC 2/8] fs/ext4: Disallow verity if inode is DAX

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Message-ID: <20200415120002.GE6126@quack2.suse.cz>
Date:   Wed, 15 Apr 2020 14:00:02 +0200
From:   Jan Kara <jack@...e.cz>
To:     ira.weiny@...el.com
Cc:     linux-kernel@...r.kernel.org, Jan Kara <jack@...e.cz>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jeff Moyer <jmoyer@...hat.com>,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH RFC 2/8] fs/ext4: Disallow verity if inode is DAX

On Mon 13-04-20 21:00:24, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
> 
> Verity and DAX are incompatible.  Changing the DAX mode due to a verity
> flag change is wrong without a corresponding address_space_operations
> update.
> 
> Make the 2 options mutually exclusive by returning an error if DAX was
> set first.
> 
> (Setting DAX is already disabled if Verity is set first.)
> 
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> ---
>  fs/ext4/verity.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/ext4/verity.c b/fs/ext4/verity.c
> index dc5ec724d889..ce3f9a198d3b 100644
> --- a/fs/ext4/verity.c
> +++ b/fs/ext4/verity.c
> @@ -113,6 +113,9 @@ static int ext4_begin_enable_verity(struct file *filp)
>  	handle_t *handle;
>  	int err;
>  
> +	if (WARN_ON_ONCE(IS_DAX(inode)))
> +		return -EINVAL;
> +

Hum, one question, is there a reason for WARN_ON_ONCE()? If I understand
correctly, user could normally trigger this, couldn't he?

								Honza

>  	if (ext4_verity_in_progress(inode))
>  		return -EBUSY;
>  
> -- 
> 2.25.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR