Re: [PATCH 2/4 v6] lib: debugobjects: add global free list and the counter

[Yang Shi]

On 2/13/18 2:02 AM, Thomas Gleixner wrote:
> On Mon, 12 Feb 2018, Yang Shi wrote:
> > On 2/12/18 8:25 AM, Thomas Gleixner wrote:
> > > On Tue, 6 Feb 2018, Yang Shi wrote:
> > > > +	/*
> > > > +	 * Reuse objs from the global free list, they will be reinitialized
> > > > +	 * when allocating
> > > > +	 */
> > > > +	while (obj_nr_tofree > 0 && (obj_pool_free < obj_pool_min_free)) {
> > > > +		raw_spin_lock_irqsave(&pool_lock, flags);
> > > > +		obj = hlist_entry(obj_to_free.first, typeof(*obj), node);
> > > This is racy vs. the worker thread. Assume obj_nr_tofree = 1:
> > >
> > > CPU0					CPU1
> > > worker
> > >      lock(&pool_lock);			while (obj_nr_tofree > 0 && ...) {
> > >        obj = hlist_entry(obj_to_free);	  lock(&pool_lock);
> > >        hlist_del(obj);			
> > >        obj_nr_tofree--;
> > >        ...
> > >      unlock(&pool_lock);
> > > 					  obj = hlist_entry(obj_to_free);
> > > 					  hlist_del(obj); <------- NULL
> > > pointer dereference
> > >
> > > Not what you want, right? The counter or the list head need to be rechecked
> > > after the lock is acquired.
> > Yes, you are right. Will fix the race in newer version.
> I fixed up all the minor issues with this series and applied it to:
>
>     git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git core/debugobjects
>
> Please double check the result.

Thanks a lot. It looks good.

Regards,
Yang

> Thanks,
>
> 	tglx