Re: slub/debugobjects: lockup when freeing memory

[Thomas Gleixner <tglx@linutronix.de>]

On Thu, 19 Jun 2014, Paul E. McKenney wrote:

> On Thu, Jun 19, 2014 at 10:37:17PM +0200, Thomas Gleixner wrote:
> > On Thu, 19 Jun 2014, Paul E. McKenney wrote:
> > > On Thu, Jun 19, 2014 at 09:29:08PM +0200, Thomas Gleixner wrote:
> > > > On Thu, 19 Jun 2014, Paul E. McKenney wrote:
> > > > Well, no. Look at the callchain:
> > > > 
> > > > __call_rcu
> > > >     debug_object_activate
> > > >        rcuhead_fixup_activate
> > > >           debug_object_init
> > > >               kmem_cache_alloc
> > > > 
> > > > So call rcu activates the object, but the object has no reference in
> > > > the debug objects code so the fixup code is called which inits the
> > > > object and allocates a reference ....
> > > 
> > > OK, got it.  And you are right, call_rcu() has done this for a very
> > > long time, so not sure what changed.  But it seems like the right
> > > approach is to provide a debug-object-free call_rcu_alloc() for use
> > > by the memory allocators.
> > > 
> > > Seem reasonable?  If so, please see the following patch.
> > 
> > Not really, you're torpedoing the whole purpose of debugobjects :)
> > 
> > So, why can't we just init the rcu head when the stuff is created?
> 
> That would allow me to keep my code unchanged, so I am in favor.  ;-)

Almost unchanged. You need to provide a function to do so, i.e. make
use of

    debug_init_rcu_head()

Thanks,

	tglx