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

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Message-ID: <4df6c3c1-7d52-6bfa-9b0d-365de5332c06@linux.ibm.com>
Date:   Mon, 3 Jan 2022 11:36:58 +0100
From:   Karsten Graul <kgraul@...ux.ibm.com>
To:     Wen Gu <guwen@...ux.alibaba.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

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.
> What do you think about it?
> 

Hi Wen,

thank you, and I also wish you and your family a happy New Year!

Thanks for your detailed explanation, you convinced me of your idea to use
a reference counting! I think its a good solution for the various problems you describe.

I am still thinking that even if you saw no problems when conn->lgr is not NULL when the lgr
is already terminated there should be more attention on the places where conn->lgr is checked.
For example, in smc_cdc_get_slot_and_msg_send() there is a check for !conn->lgr with the intention
to avoid working with a terminated link group.
Should all checks for !conn->lgr be now replaced by the check for conn->freed ?? Does this make sense?