linux-kernel - Re: [PATCH v2 net] net/smc: postpone sk

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Message-ID: <6b79fd16-79dd-450f-7eb7-ba5d6be2be0c@linux.ibm.com>
Date:   Tue, 24 May 2022 14:05:26 +0200
From:   Karsten Graul <kgraul@...ux.ibm.com>
To:     liuyacan@...p.netease.com
Cc:     davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        netdev@...r.kernel.org, pabeni@...hat.com, ubraun@...ux.ibm.com
Subject: Re: [PATCH v2 net] net/smc: postpone sk_refcnt increment in connect()

On 23/05/2022 17:21, liuyacan@...p.netease.com wrote:
>>>> This is a rather unusual problem that can come up when fallback=true BEFORE smc_connect()
>>>> is called. But nevertheless, it is a problem.
>>>>
>>>> Right now I am not sure if it is okay when we NOT hold a ref to smc->sk during all fallback
>>>> processing. This change also conflicts with a patch that is already on net-next (3aba1030).
>>>
>>> Do you mean put the ref to smc->sk during all fallback processing unconditionally and remove 
>>> the fallback branch sock_put() in __smc_release()?
>>
>> What I had in mind was to eventually call sock_put() in __smc_release() even if sk->sk_state == SMC_INIT
>> (currently the extra check in the if() for sk->sk_state != SMC_INIT prevents the sock_put()), but only
>> when it is sure that we actually reached the sock_hold() in smc_connect() before.
>>
>> But maybe we find out that the sock_hold() is not needed for fallback sockets, I don't know...
> 
> I do think the sock_hold()/sock_put() for smc->sk is a bit complicated, Emm, I'm not sure if it 
> can be simplified..
> 
> In fact, I'm sure there must be another ref count issue in my environment,but I haven't caught it yet.
> 

Can you check my latest mail from a minute ago in thread
"Re: [PATCH net-next v2] net/smc: align the connect behaviour with TCP"
I think this answer also affects our discussion.