Re: [PATCH V11 11/11] fs/xfs: Update xfs_ioctl_setattr_dax_invalidate()

[Jan Kara]

On Tue 02-06-20 10:23:53, Darrick J. Wong wrote:
> On Tue, Apr 28, 2020 at 01:11:38PM -0700, Darrick J. Wong wrote:
> > > -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?

You have to have an equivalent of write access to the file to be able to
trigger d_mark_dontcache(). So you can e.g. delete it.  Or you could
fadvise / madvise regarding its page cache. I don't see the ability to push
inode out of cache as stronger than the abilities you already have...

								Honza
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR