netdev - Re: [PATCH net] net/smc: fix NULL sndbuf_desc in smc_cdc_tx

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Date:   Tue, 07 Mar 2023 08:27:07 -0800
From:   Alexander H Duyck <alexander.duyck@...il.com>
To:     Wenjia Zhang <wenjia@...ux.ibm.com>,
        "D. Wythe" <alibuda@...ux.alibaba.com>, kgraul@...ux.ibm.com,
        jaka@...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] net/smc: fix NULL sndbuf_desc in
 smc_cdc_tx_handler()

On Mon, 2023-03-06 at 22:06 +0100, Wenjia Zhang wrote:
> 
> On 06.03.23 17:38, Alexander H Duyck wrote:
> > On Mon, 2023-03-06 at 11:36 +0800, D. Wythe wrote:
> > > From: "D. Wythe" <alibuda@...ux.alibaba.com>
> > > 
> > > When performing a stress test on SMC-R by rmmod mlx5_ib driver
> > > during the wrk/nginx test, we found that there is a probability
> > > of triggering a panic while terminating all link groups.
> > > 
> > > This issue dues to the race between smc_smcr_terminate_all()
> > > and smc_buf_create().
> > > 
> > > 			smc_smcr_terminate_all
> > > 
> > > smc_buf_create
> > > /* init */
> > > conn->sndbuf_desc = NULL;
> > > ...
> > > 
> > > 			__smc_lgr_terminate
> > > 				smc_conn_kill
> > > 					smc_close_abort
> > > 						smc_cdc_get_slot_and_msg_send
> > > 
> > > 			__softirqentry_text_start
> > > 				smc_wr_tx_process_cqe
> > > 					smc_cdc_tx_handler
> > > 						READ(conn->sndbuf_desc->len);
> > > 						/* panic dues to NULL sndbuf_desc */
> > > 
> > > conn->sndbuf_desc = xxx;
> > > 
> > > This patch tries to fix the issue by always to check the sndbuf_desc
> > > before send any cdc msg, to make sure that no null pointer is
> > > seen during cqe processing.
> > > 
> > > Fixes: 0b29ec643613 ("net/smc: immediate termination for SMCR link groups")
> > > Signed-off-by: D. Wythe <alibuda@...ux.alibaba.com>
> > 
> > Looking at the code for __smc_buf_create it seems like you might have
> > more issues hiding in the code. From what I can tell smc_buf_get_slot
> > can only return a pointer or NULL but it is getting checked for being
> > being a PTR_ERR or IS_ERR in several spots that are likely all dead
> > code.
> > 
> This smc_buf_get_slot() is used to get a reusable slot, which is 
> originally assigned by smcr_new_buf_create() or smcd_new_buf_create() 
> depending on the device being used. In 
> smcr_new_buf_create()/smcd_new_buf_create(), the pointer values of the 
> return codes are converted from integer values.

Ah, okay that is what I was missing.