linux-kernel - Re: [PATCH net] net/smc: fix listen processing for SMC-Rv2

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Message-Id: <20220523121245.1910773-1-liuyacan@corp.netease.com>
Date:   Mon, 23 May 2022 20:12:45 +0800
From:   liuyacan@...p.netease.com
To:     kgraul@...ux.ibm.com
Cc:     davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        liuyacan@...p.netease.com, netdev@...r.kernel.org,
        pabeni@...hat.com, ubraun@...ux.ibm.com
Subject: Re: [PATCH net] net/smc: fix listen processing for SMC-Rv2

> > From: liuyacan <liuyacan@...p.netease.com>
> > 
> > In the process of checking whether RDMAv2 is available, the current
> > implementation first sets ini->smcrv2.ib_dev_v2, and then allocates
> > smc buf desc, but the latter may fail. Unfortunately, the caller
> > will only check the former. In this case, a NULL pointer reference
> > will occur in smc_clc_send_confirm_accept() when accessing
> > conn->rmb_desc.
> > 
> > This patch does two things:
> > 1. Use the return code to determine whether V2 is available.
> > 2. If the return code is NODEV, continue to check whether V1 is
> > available.
> > 
> > Fixes: e49300a6bf62 ("net/smc: add listen processing for SMC-Rv2")
> > Signed-off-by: liuyacan <liuyacan@...p.netease.com>
> > ---
>
> I am not happy with this patch. You are right that this is a problem,
> but the fix should be much simpler: set ini->smcrv2.ib_dev_v2 = NULL in
> smc_find_rdma_v2_device_serv() after the not_found label, just like it is
> done in a similar way for the ISM device in smc_find_ism_v1_device_serv().
>
> Your patch changes many more things, and beside that you eliminated the calls 
> to smc_find_ism_store_rc() completely, which is not correct.
> 
> Since your patch was already applied (btw. 3:20 hours after you submitted it),
> please revert it and resend. Thank you.

I also have considered this way, one question is that do we need to do more roll 
back work before V1 check? 

Specifically, In smc_find_rdma_v2_device_serv(), there are the following steps:

1. smc_listen_rdma_init()
   1.1 smc_conn_create()
   1.2 smc_buf_create()   --> may fail
2. smc_listen_rdma_reg()  --> may fail

When later steps fail, Do we need to roll back previous steps?
Thank you.