linux-kernel - Re: [PATCH V4 1/8] fs/ext4: Narrow scope of DAX check in setflags

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Date:   Fri, 22 May 2020 09:58:19 +0200
From:   Jan Kara <jack@...e.cz>
To:     ira.weiny@...el.com
Cc:     linux-ext4@...r.kernel.org,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>,
        Eric Biggers <ebiggers@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>, Jeff Moyer <jmoyer@...hat.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4 1/8] fs/ext4: Narrow scope of DAX check in setflags

On Thu 21-05-20 12:13:06, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
> 
> When preventing DAX and journaling on an inode.  Use the effective DAX
> check rather than the mount option.
> 
> This will be required to support per inode DAX flags.
> 
> Reviewed-by: Jan Kara <jack@...e.cz>
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
...
> diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
> index bfc1281fc4cb..5813e5e73eab 100644
> --- a/fs/ext4/ioctl.c
> +++ b/fs/ext4/ioctl.c
> @@ -393,9 +393,9 @@ static int ext4_ioctl_setflags(struct inode *inode,
>  	if ((jflag ^ oldflags) & (EXT4_JOURNAL_DATA_FL)) {
>  		/*
>  		 * Changes to the journaling mode can cause unsafe changes to
> -		 * S_DAX if we are using the DAX mount option.
> +		 * S_DAX if the inode is DAX
>  		 */
> -		if (test_opt(inode->i_sb, DAX)) {
> +		if (IS_DAX(inode)) {
>  			err = -EBUSY;
>  			goto flags_out;
>  		}

Now one problem popped up in my mind: We should also make EXT4_JOURNAL_DATA_FL
and EXT4_DAX_FL exclusive so that both cannot be turned on at the same
time. And IS_DAX() check isn't enough for that. Sorry for not noticing
earlier... it's like peeling an onion...

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR