netdev - Re: netfilter: active obj WARN when cleaning up

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Date:	Wed, 27 Nov 2013 14:44:58 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
cc:	Pablo Neira Ayuso <pablo@...filter.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	Patrick McHardy <kaber@...sh.net>, kadlec@...ckhole.kfki.hu,
	"David S. Miller" <davem@...emloft.net>,
	netfilter-devel@...r.kernel.org, coreteam@...filter.org,
	netdev@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Greg KH <greg@...ah.com>
Subject: Re: netfilter: active obj WARN when cleaning up

On Wed, 27 Nov 2013, Russell King - ARM Linux wrote:

> On Wed, Nov 27, 2013 at 01:32:31PM +0000, Russell King - ARM Linux wrote:
> > On Wed, Nov 27, 2013 at 02:29:41PM +0100, Thomas Gleixner wrote:
> > > Though the kobject is the only thing which has a delayed work embedded
> > > inside struct kmem_cache. And the debug object splat points at the
> > > kmem_cache_free() of the struct kmem_cache itself. That's why I
> > > assumed the wreckage around that place. And indeed:
> > > 
> > > kmem_cache_destroy(s)
> > >     __kmem_cache_shutdown(s)
> > >       sysfs_slab_remove(s)
> > >         ....
> > > 	kobject_put(&s->kobj)
> > >            kref_put(&kobj->kref, kobject_release);
> > > 	     kobject_release(kref)
> > >     	       #ifdef CONFIG_DEBUG_KOBJECT_RELEASE
> > > 	         schedule_delayed_work(&kobj->release)
> > > 	       #else
> > > 	        kobject_cleanup(kobj)
> > > 	       #endif
> > > 
> > > So in the CONFIG_DEBUG_KOBJECT_RELEASE=y case, schedule_delayed_work()
> > > _IS_ called which arms the timer. debugobjects catches the attempt to
> > > free struct kmem_cache which contains the armed timer.
> > 
> > You fail to show where the free is in the above path.
> 
> Right, there's a kmem_cache_free(kmem_cache, s); by the slob code
> after the above sequence, which is The Bug(tm).
> 
> As I said, a kobject has its own lifetime.  If you embed that into
> another structure, that structure inherits the lifetime of the kobject,
> which is from the point at which it's created to the point at which the
> kobject's release function is called.
> 
> So no, the code here is buggy.  The kobject debugging has yet again
> found a violation of the kobject lifetime rules.  slub needs fixing.

I leave that discussion to you, greg and the slub folks.

/me prepares deck chair, drinks and popcorn 
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