Re: panic: ifc_free_unit: bit is already cleared

On Thu, Oct 06, 2005 at 10:09:50AM +1300, Andrew Thompson 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.
> 
> I dont think this is the problem. IF_CLONE_REMREF(ifc) is freeing
> ifc->ifc_units in if_clone_detach(). It look like the ref counting isnt
> working quite right.

FWIW, I tried to look at the $subject problem since I had had it
before, but just got a different panic:

        Memory modified after free 0xc140b000(4092) val=deadc0dc _at_ 0xc140b000
        panic: Most recently used by clone

The clone code seems to have decremented something (refcount?) twice
after freeing the memory chunk.

-- 
Yar