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Subject: Re: [PATCH] netfilter: nf_ct_helper: Fix possible panic when
 nf_conntrack_helper_unregister is used in an unloadable module
To:     Su Yanjun <suyanjun218@163.com>, pablo@netfilter.org,
        kadlec@blackhole.kfki.hu, fw@strlen.de, davem@davemloft.net,
        netfilter-devel@vger.kernel.org, coreteam@netfilter.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     suyj.fnst@cn.fujitsu.com
References: <1551419766-1039-1-git-send-email-suyanjun218@163.com>
From:   Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Message-ID: <e420b6c0-bebf-a2fc-a2ee-7b3e0023d833@cogentembedded.com>
Date:   Fri, 1 Mar 2019 11:43:43 +0300
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Hello!

On 01.03.2019 8:56, Su Yanjun wrote:

> From: Su Yanjun <suyj.fnst@cn.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?

> 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?

> situation.
> 
> Signed-off-by: Su Yanjun <suyj.fnst@cn.fujitsu.com>
[...]

MBR, Sergei