linux-ext4 - Re: [PATCH v3 06/12] fs/xfs: Check if the inode supports DAX under lock

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Date:   Wed, 12 Feb 2020 08:10:42 -0800
From:   Ira Weiny <ira.weiny@...el.com>
To:     Dave Chinner <david@...morbit.com>
Cc:     linux-kernel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Christoph Hellwig <hch@....de>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v3 06/12] fs/xfs: Check if the inode supports DAX under
 lock

On Wed, Feb 12, 2020 at 07:42:20AM +1100, Dave Chinner wrote:
> On Tue, Feb 11, 2020 at 09:55:09AM -0800, Ira Weiny wrote:
> > On Tue, Feb 11, 2020 at 05:16:39PM +1100, Dave Chinner wrote:
> > > On Sat, Feb 08, 2020 at 11:34:39AM -0800, ira.weiny@...el.com wrote:
> > > > From: Ira Weiny <ira.weiny@...el.com>
> > > > 

[snip]

> > > 
> > > This raciness in checking the DAX flags is the reason that
> > > xfs_ioctl_setattr_xflags() redoes all the reflink vs dax checks once
> > > it's called under the XFS_ILOCK_EXCL during the actual change
> > > transaction....
> > 
> > Ok I found this by trying to make sure that the xfs_inode_supports_dax() call
> > was always returning valid data.  So I don't have a specific test which was
> > failing.
> > 
> > Looking at the code again, it sounds like I was wrong about which locks protect
> > what and with your explanation above it looks like there is nothing to be done
> > here and I can drop the patch.
> > 
> > Would you agree?
> 
> *nod*

Thanks! done.
Ira

> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@...morbit.com