netdev - Re: [PATCH net v2 2/2] net/smc: correct the reason code in smc_listen_find

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Message-ID: <20231018070142.GY92403@linux.alibaba.com>
Date: Wed, 18 Oct 2023 15:01:42 +0800
From: Dust Li <dust.li@...ux.alibaba.com>
To: Guangguan Wang <guangguan.wang@...ux.alibaba.com>, kgraul@...ux.ibm.com,
	wenjia@...ux.ibm.com, jaka@...ux.ibm.com, davem@...emloft.net,
	edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com
Cc: tonylu@...ux.alibaba.com, alibuda@...ux.alibaba.com,
	guwen@...ux.alibaba.com, linux-s390@...r.kernel.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v2 2/2] net/smc: correct the reason code in
 smc_listen_find_device when fallback

On Tue, Oct 17, 2023 at 08:42:34PM +0800, Guangguan Wang wrote:
>The ini->rc is used to store the last error happened when finding usable
>ism or rdma device in smc_listen_find_device, and is set by calling smc_
>find_device_store_rc. Once the ini->rc is assigned to an none-zero value,
>the value can not be overwritten anymore. So the ini-rc should be set to
>the error reason only when an error actually occurs.
>
>When finding ISM/RDMA devices, device not found is not a real error, as
>not all machine have ISM/RDMA devices. Failures after device found, when
>initializing device or when initializing connection, is real errors, and
>should be store in ini->rc.
>
>SMC_CLC_DECL_DIFFPREFIX also is not a real error, as for SMC-RV2, it is
>not require same prefix.
>
>Signed-off-by: Guangguan Wang <guangguan.wang@...ux.alibaba.com>
>---
> net/smc/af_smc.c | 12 +++---------
> 1 file changed, 3 insertions(+), 9 deletions(-)
>
>diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
>index b3a67a168495..21e9c6ec4d01 100644
>--- a/net/smc/af_smc.c
>+++ b/net/smc/af_smc.c
>@@ -2163,10 +2163,8 @@ static void smc_find_ism_v2_device_serv(struct smc_sock *new_smc,
> 	}
> 	mutex_unlock(&smcd_dev_list.mutex);
> 
>-	if (!ini->ism_dev[0]) {
>-		smc_find_device_store_rc(SMC_CLC_DECL_NOSMCD2DEV, ini);
>+	if (!ini->ism_dev[0])

Hi Guangguan,

Generally, I think this is right. Fallback in one kind of device should
not be the final fallback reason.

But what if we have more than one device and failed more than once, for
example:
Let's say we have an ISM device, a RDMA device. First we looked the ISM device
and failed during the initialization, we got a fallback reason A. Then we
looked for the RDMA device, and failed again, with another reason B.
Finally, we fallback to TCP. What should fallback reason be ?

OTOH, SMC_CLC_DECL_NOSMCD2DEV is only used here. Removing it would mean
that we would never see SMC_CLC_DECL_NOSMCD2DEV in the fallback reason,
which makes it meaningless.

Best regards,
Dust

> 		goto not_found;
>-	}
> 
> 	smc_ism_get_system_eid(&eid);
> 	if (!smc_clc_match_eid(ini->negotiated_eid, smc_v2_ext,
>@@ -2216,9 +2214,9 @@ static void smc_find_ism_v1_device_serv(struct smc_sock *new_smc,
> 	rc = smc_listen_ism_init(new_smc, ini);
> 	if (!rc)
> 		return;		/* V1 ISM device found */
>+	smc_find_device_store_rc(rc, ini);
> 
> not_found:
>-	smc_find_device_store_rc(rc, ini);
> 	ini->smcd_version &= ~SMC_V1;
> 	ini->ism_dev[0] = NULL;
> 	ini->is_smcd = false;
>@@ -2267,10 +2265,8 @@ static void smc_find_rdma_v2_device_serv(struct smc_sock *new_smc,
> 	ini->smcrv2.saddr = new_smc->clcsock->sk->sk_rcv_saddr;
> 	ini->smcrv2.daddr = smc_ib_gid_to_ipv4(smc_v2_ext->roce);
> 	rc = smc_find_rdma_device(new_smc, ini);
>-	if (rc) {
>-		smc_find_device_store_rc(rc, ini);
>+	if (rc)
> 		goto not_found;
>-	}
> 	if (!ini->smcrv2.uses_gateway)
> 		memcpy(ini->smcrv2.nexthop_mac, pclc->lcl.mac, ETH_ALEN);
> 
>@@ -2331,8 +2327,6 @@ static int smc_listen_find_device(struct smc_sock *new_smc,
> 
> 	/* check for matching IP prefix and subnet length (V1) */
> 	prfx_rc = smc_listen_prfx_check(new_smc, pclc);
>-	if (prfx_rc)
>-		smc_find_device_store_rc(prfx_rc, ini);
> 
> 	/* get vlan id from IP device */
> 	if (smc_vlan_by_tcpsk(new_smc->clcsock, ini))
>-- 
>2.24.3 (Apple Git-128)