linux-kernel - Re: [PATCH net] net/smc: return the right falback reason when prefix checks fail

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Message-ID: <1b317491-5995-4277-bcad-455bece62666@linux.alibaba.com>
Date:   Fri, 13 Oct 2023 16:38:46 +0800
From:   Guangguan Wang <guangguan.wang@...ux.alibaba.com>
To:     Wen Gu <guwen@...ux.alibaba.com>,
        Dust Li <dust.li@...ux.alibaba.com>,
        Karsten Graul <kgraul@...ux.ibm.com>,
        Wenjia Zhang <wenjia@...ux.ibm.com>,
        Jan Karcher <jaka@...ux.ibm.com>,
        "D. Wythe" <alibuda@...ux.alibaba.com>,
        Tony Lu <tonylu@...ux.alibaba.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     linux-s390@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net/smc: return the right falback reason when prefix
 checks fail



On 2023/10/13 16:00, Wen Gu wrote:
> 
> 
> On 2023/10/12 20:37, Dust Li wrote:
> 
>> In the smc_listen_work(), if smc_listen_prfx_check() failed,
>> the real reason: SMC_CLC_DECL_DIFFPREFIX was dropped, and
>> SMC_CLC_DECL_NOSMCDEV was returned.
>>
>> Althrough this is also kind of SMC_CLC_DECL_NOSMCDEV, but return
>> the real reason is much friendly for debugging.
>>
>> Fixes: e49300a6bf62 ("net/smc: add listen processing for SMC-Rv2")
>> Signed-off-by: Dust Li <dust.li@...ux.alibaba.com>
>> ---
>>   net/smc/af_smc.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
>> index bacdd971615e..21d4476b937b 100644
>> --- a/net/smc/af_smc.c
>> +++ b/net/smc/af_smc.c
>> @@ -2361,7 +2361,7 @@ static int smc_listen_find_device(struct smc_sock *new_smc,
>>           smc_find_ism_store_rc(rc, ini);
>>           return (!rc) ? 0 : ini->rc;
>>       }
>> -    return SMC_CLC_DECL_NOSMCDEV;
>> +    return prfx_rc;
>>   }
>>     /* listen worker: finish RDMA setup */
> Inspired by this fix, I am thinking that is it suitable to store the first
> decline reason rather than real decline reason that caused the return of
> smc_listen_find_device()?
> 
> For example, when running SMC between two peers with only RDMA devices. Then
> in smc_listen_find_device():
> 
> 1. call smc_find_ism_v2_device_serv() and find that no ISMv2 can be used.
>    the reason code will be stored as SMC_CLC_DECL_NOSMCD2DEV.
> 
> ...
> 
> 2. call smc_find_rdma_v1_device_serv() and find a RDMA device, but somehow
>    it failed to create buffers. It should inform users that SMC_CLC_DECL_MEM
>    occurs, but now the reason code returned SMC_CLC_DECL_NOSMCD2DEV.
> 
> I think users may be confused that why peer declines with this reason and
> wonder what happens when trying to use SMC-R.

Yes, the reason code here also makes me confused.
I think it is caused by not correctly using the function smc_find_ism_store_rc.
I'm working for the fix.

> 
> 
> Thanks,
> Wen Gu
>