linux-kernel - Re: [PATCH V11 11/11] fs/xfs: Update xfs_ioctl_setattr_dax

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Date:   Tue, 2 Jun 2020 16:15:10 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        Al Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>,
        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-fsdevel@...r.kernel.org,
        linux-api@...r.kernel.org
Subject: Re: [PATCH V11 11/11] fs/xfs: Update
 xfs_ioctl_setattr_dax_invalidate()

On Tue, Jun 02, 2020 at 10:23:53AM -0700, Darrick J. Wong wrote:
> On Tue, Apr 28, 2020 at 01:11:38PM -0700, Darrick J. Wong wrote:
> > On Mon, Apr 27, 2020 at 05:21:42PM -0700, ira.weiny@...el.com wrote:
> > > From: Ira Weiny <ira.weiny@...el.com>
> > > 

...

> > > -out_unlock:
> > > -	xfs_iunlock(ip, XFS_MMAPLOCK_EXCL | XFS_IOLOCK_EXCL);
> > > -	return error;
> > > +	if ((mp->m_flags & XFS_MOUNT_DAX_ALWAYS) ||
> > > +	    (mp->m_flags & XFS_MOUNT_DAX_NEVER))
> > > +		return;
> > >  
> > > +	if (((fa->fsx_xflags & FS_XFLAG_DAX) &&
> > > +	    !(ip->i_d.di_flags2 & XFS_DIFLAG2_DAX)) ||
> > > +	    (!(fa->fsx_xflags & FS_XFLAG_DAX) &&
> > > +	     (ip->i_d.di_flags2 & XFS_DIFLAG2_DAX)))
> > > +		d_mark_dontcache(inode);
> 
> Now that I think about this further, are we /really/ sure that we want
> to let unprivileged userspace cause inode evictions?

This code only applies to files they have access to.  And it does not directly
cause an eviction.  It only hints that those inodes (for which they have access
to) will not be cached thus causing them to be reloaded sooner than they might
otherwise be.

So I think we are fine here.

Ira

> 
> --D
>