netdev - Re: [PATCH net-next] net/smc: Fix smc-r link reference count

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Message-ID: <90cf2e6b-e409-7f52-bde3-ebb93994b931@linux.alibaba.com>
Date:   Fri, 6 May 2022 17:47:29 +0800
From:   "D. Wythe" <alibuda@...ux.alibaba.com>
To:     Wen Gu <guwen@...ux.alibaba.com>, kgraul@...ux.ibm.com
Cc:     kuba@...nel.org, davem@...emloft.net, netdev@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: Re: [PATCH net-next] net/smc: Fix smc-r link reference count



在 2022/5/6 下午3:58, Wen Gu 写道:

> Thanks for your analysis.
> 
> 1) Is the patch more appropriate to 'net' ?

That's my mistake.

> 2) The refcnt of smc link will be
> 
>     - initilized to 1 in smcr_link_init();
> 
>     - increased when connections assigned to the link;
>       eg. smc_conn_create() or smc_switch_link_and_count();
> 
>     - decreased when connections removed from the link or link is cleared,
>       eg. smc_conn_free(), smc_switch_link_and_count(), smcr_link_clear().
> 
>     I see the theoretical race between smcr_link_hold() and 
> smcr_link_put(). Have you encountered this
>     issue in actual test, such as triggering WARN of refcount_inc()? 
> Because IMHO the race window is small
>     (link state will turned to SMC_LNK_UNUSED after smcr_link_put() and 
> connections will not be assigned to it).
> 
> 

Got your point, this race may happened with our another radical change. 
At present, this patch may not be needed.


Thanks.
D. Wythe