netdev - Re: [PATCH net] net/smc: Avoid setting clcsock options after clcsock released

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Date:   Thu, 13 Jan 2022 16:23:59 +0800
From:   Wen Gu <guwen@...ux.alibaba.com>
To:     Karsten Graul <kgraul@...ux.ibm.com>, davem@...emloft.net,
        kuba@...nel.org
Cc:     linux-s390@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net/smc: Avoid setting clcsock options after clcsock
 released

Thanks for your reply.

On 2022/1/12 5:38 pm, Karsten Graul wrote:
> On 11/01/2022 17:34, Wen Gu wrote:
>> Thanks for your reply.
>>
>> On 2022/1/11 6:03 pm, Karsten Graul wrote:
>>> On 10/01/2022 10:38, Wen Gu wrote:
>>>> We encountered a crash in smc_setsockopt() and it is caused by
>>>> accessing smc->clcsock after clcsock was released.
> 
> I like the idea to use RCU with rcu_assign_pointer() to protect that pointer!
> 
> Lets go with your initial patch (improved to address the access in smc_switch_to_fallback())
> for now because it solves your current problem.
> 

OK, I will improve the patch, adding check before clcsock access in smc_switch_to_fallback()
and return an error (-EBADF) if smc->clcsock is NULL. The caller of smc_switch_to_fallback()
will check the return value to identify whether fallback is possible.

> I put that RCU thing on our list, but if either of us here starts working on that please let the
> others know so we don't end up doing parallel work on this. But I doubt that we will be able to start working
> on that soon.
> 
> Thanks for the good idea!

Thank you! If I start working on the RCU things, I will send a RFC to let you know.

Thanks,
Wen Gu