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Message-ID: <cd996f1e-5ebf-c253-6a87-ce0e055b84c8@linux.alibaba.com>
Date:   Thu, 22 Sep 2022 16:29:34 +0800
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Subject: Re: [PATCH net] net/smc: Stop the CLC flow if no link to map buffers
 on
From:   Wen Gu <guwen@linux.alibaba.com>
To:     kgraul@linux.ibm.com, wenjia@linux.ibm.com
Cc:     linux-s390@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <1663656189-32090-1-git-send-email-guwen@linux.alibaba.com>
In-Reply-To: <1663656189-32090-1-git-send-email-guwen@linux.alibaba.com>
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On 2022/9/20 14:43, Wen Gu wrote:

> There might be a potential race between SMC-R buffer map and
> link group termination.
> 
> smc_smcr_terminate_all()     | smc_connect_rdma()
> --------------------------------------------------------------
>                               | smc_conn_create()
> for links in smcibdev        |
>          schedule links down  |
>                               | smc_buf_create()
>                               |  \- smcr_buf_map_usable_links()
>                               |      \- no usable links found,
>                               |         (rmb->mr = NULL)
>                               |
>                               | smc_clc_send_confirm()
>                               |  \- access conn->rmb_desc->mr[]->rkey
>                               |     (panic)
> 
> During reboot and IB device module remove, all links will be set
> down and no usable links remain in link groups. In such situation
> smcr_buf_map_usable_links() should return an error and stop the
> CLC flow accessing to uninitialized mr.
> 
> Fixes: b9247544c1bc ("net/smc: convert static link ID instances to support multiple links")
> Signed-off-by: Wen Gu <guwen@linux.alibaba.com>
> ---
>   net/smc/smc_core.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c
> index ebf56cd..df89c2e 100644
> --- a/net/smc/smc_core.c
> +++ b/net/smc/smc_core.c
> @@ -2239,7 +2239,7 @@ static struct smc_buf_desc *smcr_new_buf_create(struct smc_link_group *lgr,
>   static int smcr_buf_map_usable_links(struct smc_link_group *lgr,
>   				     struct smc_buf_desc *buf_desc, bool is_rmb)
>   {
> -	int i, rc = 0;
> +	int i, rc = 0, cnt = 0;
>   
>   	/* protect against parallel link reconfiguration */
>   	mutex_lock(&lgr->llc_conf_mutex);
> @@ -2252,9 +2252,12 @@ static int smcr_buf_map_usable_links(struct smc_link_group *lgr,
>   			rc = -ENOMEM;
>   			goto out;
>   		}
> +		cnt++;
>   	}
>   out:
>   	mutex_unlock(&lgr->llc_conf_mutex);
> +	if (!rc && !cnt)
> +		rc = -EINVAL;
>   	return rc;
>   }
>   

Any comments or reviews are welcome and appreciated.

Thanks,
Wen Gu