linux-kernel - Re: [PATCH] netfilter: nf_ct_helper: Fix possible panic when nf_conntrack_helper_unregister is used in an unloadable module

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Message-ID: <ddd00e53-266b-93cc-898f-d92b88366d4d@cn.fujitsu.com>
Date:   Fri, 1 Mar 2019 17:08:23 +0800
From:   "Su Yanjun <suyj.fnst@...fujitsu.com>" <suyj.fnst@...fujitsu.com>
To:     Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        Su Yanjun <suyanjun218@....com>, <pablo@...filter.org>,
        <kadlec@...ckhole.kfki.hu>, <fw@...len.de>, <davem@...emloft.net>,
        <netfilter-devel@...r.kernel.org>, <coreteam@...filter.org>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] netfilter: nf_ct_helper: Fix possible panic when
 nf_conntrack_helper_unregister is used in an unloadable module


On 2019/3/1 16:43, Sergei Shtylyov wrote:
> Hello!
>
> On 01.03.2019 8:56, Su Yanjun wrote:
>
>> From: Su Yanjun <suyj.fnst@...fujitsu.com>
>>
>> Because nf_conntrack_helper_unregister maybe used in an unloadable 
>> module,
>> it uses 'synchronize_rcu' which may cause kernel panic.
>>
>> According to the artical:
>
>    Article?
>
I got it.
>> RCU and Unloadable Modules
>> https://lwn.net/Articles/217484/
>>
>> When we have a heavy rcu callback load, then some of the callbacks 
>> might be
>> deferred in order to allow other processing to proceed. 
>> sychnorize_rcu does
>> not wait rcu callback complete and module may be unloaded before 
>> callback
>> done.
>>
>> This patch uses rcu_barrier instead of synchronize_rcu will prevent this
>                                                         ^ that/which 
> missed?
>
Yes.
>> situation.
>>
>> Signed-off-by: Su Yanjun <suyj.fnst@...fujitsu.com>
> [...]
>
> MBR, Sergei
>
>
Thanks.

Su