Re: panic: ifc_free_unit: bit is already cleared

On Mon, Oct 10, 2005 at 03:28:49AM +0400, Yar Tikhiy wrote:
> 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.

Yes, it still clears the interface bit in ifc_units in ifc_free_unit()
after freeing the memory (for if_vlan and if_stf).

I want to change the refcounting to count the number of cloned
interfaces and have been playing with the code. The main problem is when
a module is unloaded it doesnt use the if_clone* routines when destoying
the interfaces in the simple_clone case. 


Andrew