panic: ifc_free_unit: bit is already cleared

[Brooks Davis]

On Tue, Oct 11, 2005 at 08:41:16AM +0200, Pawel Jakub Dawidek wrote:
> On Wed, Oct 05, 2005 at 01:55:15PM -0700, Brooks Davis wrote:
> +> On Wed, Oct 05, 2005 at 10:36:39PM +0200, Pawel Jakub Dawidek wrote:
> +> > On Wed, Oct 05, 2005 at 03:49:03PM +1300, Andrew Thompson wrote:
> +> > +> Hi,
> +> > +> 
> +> > +> I have found a repeatable panic with network device cloning, unfortunatly I am
> +> > +> unable to dump on this box. This is sparc64 with a 2 day old current.
> +> > 
> +> > The order is wrong in vlan_modevent().
> +> > 
> +> > if_clone_detach() is freeing ifc_units field, so ifc_free_unit() should not
> +> > be called after that.
> +> > 
> +> > This patch should fix the problem:
> +> > 
> +> > 	http://people.freebsd.org/~pjd/patches/if_vlan.c.patch
> +> 
> +> Yes.  This does introduce a race in that a new interface could
> +> be created between the vlan_clone_destroy loop and the call to
> +> if_clone_detach.  It's going to be hard to trigger, but it probably
> +> should be fixed.  Since cloning isn't performance critical, I think
> +> adding a dead flag to the clone structure and failing all attempts once
> +> the flag is set.
> 
> I think it is a low-risk patch and the race isn't really critical.
> What do you guys think about going with this fix for 6.0?
> I'm all for better fix (the one thompsa@ is working on) going to HEAD
> and 6.1, but better fix - higher risk.
> So what's your opinion?
> 
> Or maybe we will be able to create low-risk complete fix?

The race is mostly a non-issue so I'd be OK with the low-risk fix.  To
hit the race you'd have to be trying (or forget that you are running
some sort of interface management daemon).

-- Brooks

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