linux-kernel - Re: System freeze on reboot

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Date:	Thu, 3 Sep 2009 00:31:07 +0200
From:	Zdenek Kabelac <zdenek.kabelac@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Patrick McHardy <kaber@...sh.net>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Robin Holt <holt@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Jesper Dangaard Brouer <hawk@...x.dk>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Netfilter Developers <netfilter-devel@...r.kernel.org>
Subject: Re: System freeze on reboot - general protection fault

2009/9/3 Eric Dumazet <eric.dumazet@...il.com>:
> Zdenek Kabelac a écrit :
>> 2009/8/17 Patrick McHardy <kaber@...sh.net>:
>>> Eric Dumazet wrote:
>>>> Zdenek Kabelac a écrit :
>>>>>  [<ffffffffa02c502f>] nf_conntrack_ftp_fini+0x2f/0x70 [nf_conntrack_ftp]
>>>>>  [<ffffffff8027bcc5>] sys_delete_module+0x1a5/0x270
>>>>>  [<ffffffff8020d329>] ? retint_swapgs+0xe/0x13
>>>>>  [<ffffffff80271bf2>] ? trace_hardirqs_on_caller+0x162/0x1b0
>>>>>  [<ffffffff80292121>] ? audit_syscall_entry+0x191/0x1c0
>>>>>  [<ffffffff80526dae>] ? trace_hardirqs_on_thunk+0x3a/0x3f
>>>>>  [<ffffffff8020c84b>] system_call_fastpath+0x16/0x1b
>>>>> Code: c6 00 00 0f 82 66 ff ff ff 49 8b 9e d8 05 00 00 48 85 db 75 16
>>>>> e9 8e 00 00 00 0f 1f 44 00 00 48 85 c0 0f 84 80 00 00 00 48 89 c3 <0f>
>>>>> b6 4b 37 48 8b 03 48 8d 14 cd 00 00 00 00 0f 18 08 48 29 ca
>>>>> RIP  [<ffffffffa02b2c2c>] nf_conntrack_helper_unregister+0x16c/0x320
>>>>> [nf_conntrack]
>>>>>  RSP <ffff88013982fe68>
>>>>> CR2: 0000000000000038
>>>>> ---[ end trace bc3a0ede3d0084db ]---
>>>>>
>>>> I am currently traveling and wont be able to help you before next week.
>>>>
>>>> I added netdev, Patrick, and netfilter-devel in CC so that more eyes can take a look.
>>> Thanks for the report, I'll have a look at this. Zdenek, please
>>> send me the nf_conntrack.ko file used in the above oops. Thanks.
>>>
>>
>> Ok
>>
>> I've found the solution for my problem.
>>
>> http://thread.gmane.org/gmane.comp.security.firewalls.netfilter.devel/30483
>>
>> I've made this small fix from this thread:
>>
>> diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core
>> index b5869b9..68488f8 100644
>> --- a/net/netfilter/nf_conntrack_core.c
>> +++ b/net/netfilter/nf_conntrack_core.c
>> @@ -1108,6 +1108,7 @@ static void nf_conntrack_cleanup_init_net(void)
>>  {
>>         nf_conntrack_helper_fini();
>>         nf_conntrack_proto_fini();
>> +       rcu_barrier();
>>         kmem_cache_destroy(nf_conntrack_cachep);
>>  }
>>
>> @@ -1266,7 +1267,7 @@ static int nf_conntrack_init_init_net(void)
>>
>>         nf_conntrack_cachep = kmem_cache_create("nf_conntrack",
>>                                                 sizeof(struct nf_conn),
>> -                                               0, SLAB_DESTROY_BY_RCU, NULL);
>> +                                               0, 0, NULL);
>>         if (!nf_conntrack_cachep) {
>>                 printk(KERN_ERR "Unable to create nf_conn slab cache\n");
>>                 ret = -ENOMEM;
>>
>>
>> As the thread nf_conntrack: Use rcu_barrier() and fix kmem_cache_create flags
>> seems to be samewhat 'unfinished'  and already a bit old and I've no
>> idea whether it actually fixes problem completely or just hides it in
>> my case - I'm leaving it to some RCU gurus to fix this issue.
>>
>> All I could say is - this this extra rcu_barrier() and removal of
>> SLAB_DESTROY removes my GPF on reboot.
>>
>> Zdenek
>
> Ouch..
>
> Dont think such a patch makes your kernel better, it'll crash too.
>
> You cannot remove SLAB_DESTROY_BY_RCU like this, it's there for very good reasons.
>

Well I'm not noticing any ill behavior - also note - rcu_barrier() is
there before the cache is destroyed.
But as I said - it's just my shot into the dark - which seems to work for me...

Zdenek
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