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Subject: Re: [PATCH 3/8] vfio: add external user support
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Stephen Rothwell <sfr@canb.auug.org.au>
Date: Thu, 27 Jun 2013 19:42:46 +1000
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Cc: kvm@vger.kernel.org, linux-doc@vger.kernel.org,
 Alexey Kardashevskiy <aik@ozlabs.ru>, Alexander Graf <agraf@suse.de>,
 kvm-ppc@vger.kernel.org, linux-kernel@vger.kernel.org,
 Alex Williamson <alex.williamson@redhat.com>,
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 "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
 linuxppc-dev@lists.ozlabs.org, David Gibson <david@gibson.dropbear.id.au>
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On Thu, 2013-06-27 at 16:59 +1000, Stephen Rothwell wrote:
> > +/* Allows an external user (for example, KVM) to unlock an IOMMU
> group */
> > +static void vfio_group_del_external_user(struct file *filep)
> > +{
> > +     struct vfio_group *group = filep->private_data;
> > +
> > +     BUG_ON(filep->f_op != &vfio_group_fops);
> 
> We usually reserve BUG_ON for situations where there is no way to
> continue running or continuing will corrupt the running kernel.  Maybe
> WARN_ON() and return?

Not even that. This is a user space provided "fd", we shouldn't oops the
kernel because we passed a wrong argument, just return -EINVAL or
something like that (add a return code).

Ben.