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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Date:   Fri, 1 Mar 2019 11:43:43 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     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
Cc:     suyj.fnst@...fujitsu.com
Subject: Re: [PATCH] netfilter: nf_ct_helper: Fix possible panic when
 nf_conntrack_helper_unregister is used in an unloadable module

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?

> 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@...fujitsu.com>
[...]

MBR, Sergei