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

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Date:	Mon, 2 Dec 2013 17:18:16 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Greg KH <greg@...ah.com>
cc:	Thomas Gleixner <tglx@...utronix.de>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	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>
Subject: Re: netfilter: active obj WARN when cleaning up

On Mon, 2 Dec 2013, Greg KH wrote:

> On Mon, Dec 02, 2013 at 04:33:20PM +0000, Christoph Lameter wrote:
> > On Wed, 27 Nov 2013, Greg KH wrote:
> >
> > > Just make the kobject "dynamic" instead of embedded in struct kmem_cache
> > > and all will be fine.  I can't believe this code has been broken for
> > > this long.
> >
> > The slub code is was designed to use an embedded structure since we
> > only get the kobj  pointer passed to us from sysfs. If kobj is not
> > embedded then how can we get from the sysfs object to the kmem_cache
> > structure from the sysfs callbacks? Sysfs was designed to have embedded
> > objects as far as I can recall.
>
> Yes, it's designed to have embedded objects, so then use it that way and
> clean up the structure when the kobject goes away.  Don't use a
> different reference count for your structure than the one in the kobject
> and think that all will be fine.

We need our own reference count. So we just have to defer the
release of the kmem_cache struct until the ->release callback is
triggered. The put of the embedded kobject must be the last action on the
kmem_cache  structure which will then trigger release and that will
trigger the kmem_cache_free().



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