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Date: Thu, 12 Oct 2017 11:55:22 -0400
From: "Theodore Ts'o" <tytso@mit.edu>
To: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Jan Kara <jack@suse.cz>, linux-kernel@vger.kernel.org,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        Christoph Hellwig <hch@lst.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Chinner <david@fromorbit.com>, linux-ext4@vger.kernel.org,
        linux-nvdimm@lists.01.org
Subject: Re: [PATCH v2 2/5] ext4: prevent data corruption with journaling +
 DAX
Message-ID: <20171012155522.nqnvemlarbxxnrcw@thunk.org>
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        Ross Zwisler <ross.zwisler@linux.intel.com>,
        Jan Kara <jack@suse.cz>, linux-kernel@vger.kernel.org,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        Christoph Hellwig <hch@lst.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Chinner <david@fromorbit.com>, linux-ext4@vger.kernel.org,
        linux-nvdimm@lists.01.org
References: <20170912050526.7627-1-ross.zwisler@linux.intel.com>
 <20170912050526.7627-3-ross.zwisler@linux.intel.com>
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On Mon, Sep 11, 2017 at 11:05:23PM -0600, Ross Zwisler wrote:
> The current code has the potential for data corruption when changing an
> inode's journaling mode, as that can result in a subsequent unsafe change
> in S_DAX.
> 
> I've captured an instance of this data corruption in the following fstest:
> 
> https://patchwork.kernel.org/patch/9948377/
> 
> Prevent this data corruption from happening by disallowing changes to the
> journaling mode if the '-o dax' mount option was used.  This means that for
> a given filesystem we could have a mix of inodes using either DAX or
> data journaling, but whatever state the inodes are in will be held for the
> duration of the mount.
> 
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> Suggested-by: Jan Kara <jack@suse.cz>

Thanks, applied.

						- Ted