linux-kernel - Re: netfilter: active obj WARN when cleaning up

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Message-ID: <alpine.DEB.2.02.1311271106090.30673@ionos.tec.linutronix.de>
Date:	Wed, 27 Nov 2013 11:45:17 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Pablo Neira Ayuso <pablo@...filter.org>
cc:	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>, Russell King <linux@....linux.org.uk>
Subject: Re: netfilter: active obj WARN when cleaning up

On Wed, 27 Nov 2013, Pablo Neira Ayuso wrote:

> On Tue, Nov 26, 2013 at 02:11:57PM -0500, Sasha Levin wrote:
> > Ping? I still see this warning.
> 
> Did your test include patch 0c3c6c00c6?

And how is that patch supposed to help?
 
> > >[  418.312449] WARNING: CPU: 6 PID: 4178 at lib/debugobjects.c:260 debug_print_object+0x8d/0xb0()
> > >[  418.313243] ODEBUG: free active (active state 0) object type: timer_list hint:
> > >delayed_work_timer_fn+0x0/0x20

> > >[  418.321101]  [<ffffffff812874d7>] kmem_cache_free+0x197/0x340
> > >[  418.321101]  [<ffffffff81249e76>] kmem_cache_destroy+0x86/0xe0
> > >[  418.321101]  [<ffffffff83d5d681>] nf_conntrack_cleanup_net_list+0x131/0x170

The debug code detects an active timer, which itself is part of a
delayed work struct. The call comes from kmem_cache_destroy().

         kmem_cache_free(kmem_cache, s);

So debug object says: s contains an active timer. s is the kmem_cache
which is destroyed from nf_conntrack_cleanup_net_list.

Now struct kmem_cache has in case of SLUB:

    struct kobject kobj;    /* For sysfs */

and struct kobject has:

#ifdef CONFIG_DEBUG_KOBJECT_RELEASE
    struct delayed_work     release;
#endif

So this is the thing you want to look at:

commit c817a67ec (kobject: delayed kobject release: help find buggy
drivers) added that delayed work thing.

I fear that does not work for kobjects which are embedded into
something else.

Handing off to rmk, mm and kobject folks.

Thanks,

	tglx
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