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

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Date: Fri, 13 Oct 2023 16:00:52 +0800
From: Wen Gu <guwen@...ux.alibaba.com>
To: 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 2023/10/12 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.

Thanks,
Wen Gu