netdev - Re: [RFC PATCH net v2 1/2] net/smc: Resolve the race between link group access and termination

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Date:   Fri, 7 Jan 2022 20:04:28 +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, dust.li@...ux.alibaba.com,
        tonylu@...ux.alibaba.com
Subject: Re: [RFC PATCH net v2 1/2] net/smc: Resolve the race between link
 group access and termination

Thanks for your reply.

On 2022/1/7 5:54 pm, Karsten Graul wrote:
> On 06/01/2022 14:02, Wen Gu wrote:
>> Thanks for your reply.
>>
>> On 2022/1/5 8:03 pm, Karsten Graul wrote:
>>> On 05/01/2022 09:27, Wen Gu wrote:
>>>> On 2022/1/3 6:36 pm, Karsten Graul wrote:
>>>>> On 31/12/2021 10:44, Wen Gu wrote:
>>>>>> On 2021/12/29 8:56 pm, Karsten Graul wrote:
>>>>>>> On 28/12/2021 16:13, Wen Gu wrote:
>>>>>>>> We encountered some crashes caused by the race between the access
>>>>>>>> and the termination of link groups.
>> So I am trying this way:
>>
>> 1) Introduce a new helper smc_conn_lgr_state() to check the three stages mentioned above.
>>
>>    enum smc_conn_lgr_state {
>>           SMC_CONN_LGR_ORPHAN,    /* conn was never registered in a link group */
>>           SMC_CONN_LGR_VALID,     /* conn is registered in a link group now */
>>           SMC_CONN_LGR_INVALID,   /* conn was registered in a link group, but now
>>                                      is unregistered from it and conn->lgr should
>>                                      not be used any more */
>>    };
> 
> Sounds good, but is it really needed to separate 3 cases, i.e. who is really using them 3?
> Doesn't it come down to a more simple smc_conn_lgr_valid() which is easier to implement in
> the various places in the code? (i.e.: if (smc_conn_lgr_valid()) ....)
> Valid would mean conn->lgr != NULL and conn->alert_token_local != 0. The more special cases
> would check what they want by there own.

Yes, Most of the time we only need to check whether conn->lgr is in SMC_CONN_LGR_VALID.
Only in smc_conn_free() we need to identify whether conn->lgr is in SMC_CONN_LGR_ORPHAN
(need a directly return) or SMC_CONN_LGR_INVALID (put link group refcnt and then return).

So I agree with only checking whether conn->lgr is valid with a more simple smc_conn_lgr_valid().
And distinguish SMC_CONN_LGR_ORPHAN and SMC_CONN_LGR_INVALID cases by additional check for
conn->lgr.

Thanks,
Wen Gu