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

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Date:   Tue, 13 Feb 2018 11:02:07 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Yang Shi <yang.shi@...ux.alibaba.com>
cc:     longman@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4 v6] lib: debugobjects: add global free list and the
 counter

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,

	tglx