netdev - Re: Hung task when calling clone() due to netfilter/slab

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Date:	Wed, 1 Feb 2012 10:07:18 +0200
From:	Pekka Enberg <penberg@...nel.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Christoph Lameter <cl@...ux.com>,
	Sasha Levin <levinsasha928@...il.com>,
	Dave Jones <davej@...hat.com>, davem <davem@...emloft.net>,
	Matt Mackall <mpm@...enic.com>, kaber@...sh.net,
	pablo@...filter.org, linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, netfilter-devel@...r.kernel.org,
	netdev <netdev@...r.kernel.org>
Subject: Re: Hung task when calling clone() due to netfilter/slab

On Tue, Jan 17, 2012 at 5:30 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> Le mardi 17 janvier 2012 à 09:27 -0600, Christoph Lameter a écrit :
>
>> Subject: slub: Do not hold slub_lock when calling sysfs_slab_add()
>>
>> sysfs_slab_add() calls various sysfs functions that actually may
>> end up in userspace doing all sorts of things.
>>
>> Release the slub_lock after adding the kmem_cache structure to the list.
>> At that point the address of the kmem_cache is not known so we are
>> guaranteed exlusive access to the following modifications to the
>> kmem_cache structure.
>>
>> If the sysfs_slab_add fails then reacquire the slub_lock to
>> remove the kmem_cache structure from the list.
>>
>> Reported-by: Sasha Levin <levinsasha928@...il.com>
>> Signed-off-by: Christoph Lameter <cl@...ux.com>
>>
>> ---
>>  mm/slub.c |    3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> Index: linux-2.6/mm/slub.c
>> ===================================================================
>> --- linux-2.6.orig/mm/slub.c  2012-01-17 03:07:11.140010438 -0600
>> +++ linux-2.6/mm/slub.c       2012-01-17 03:26:06.799986908 -0600
>> @@ -3929,13 +3929,14 @@ struct kmem_cache *kmem_cache_create(con
>>               if (kmem_cache_open(s, n,
>>                               size, align, flags, ctor)) {
>>                       list_add(&s->list, &slab_caches);
>> +                     up_write(&slub_lock);
>>                       if (sysfs_slab_add(s)) {
>> +                             down_write(&slub_lock);
>>                               list_del(&s->list);
>>                               kfree(n);
>>                               kfree(s);
>>                               goto err;
>>                       }
>> -                     up_write(&slub_lock);
>>                       return s;
>>               }
>>               kfree(n);
>
> Thanks !
>
> Acked-by: Eric Dumazet <eric.dumazet@...il.com>

I'm planning to queue this for v3.4 and tagging it for -stable for
v3.3. Do we need this for older versions as well?

                        Pekka
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