netdev - [PATCH net v2] net/smc: avoid data corruption caused by decline

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Message-Id: <1700197181-83136-1-git-send-email-alibuda@linux.alibaba.com>
Date: Fri, 17 Nov 2023 12:59:41 +0800
From: "D. Wythe" <alibuda@...ux.alibaba.com>
To: kgraul@...ux.ibm.com,
	wenjia@...ux.ibm.com,
	jaka@...ux.ibm.com,
	wintera@...ux.ibm.com,
	guwen@...ux.alibaba.com
Cc: kuba@...nel.org,
	davem@...emloft.net,
	netdev@...r.kernel.org,
	linux-s390@...r.kernel.org,
	linux-rdma@...r.kernel.org,
	tonylu@...ux.alibaba.com,
	pabeni@...hat.com,
	edumazet@...gle.com
Subject: [PATCH net v2] net/smc: avoid data corruption caused by decline

From: "D. Wythe" <alibuda@...ux.alibaba.com>

We found a data corruption issue during testing of SMC-R on Redis
applications.

The benchmark has a low probability of reporting a strange error as
shown below.

"Error: Protocol error, got "\xe2" as reply type byte"

Finally, we found that the retrieved error data was as follows:

0xE2 0xD4 0xC3 0xD9 0x04 0x00 0x2C 0x20 0xA6 0x56 0x00 0x16 0x3E 0x0C
0xCB 0x04 0x02 0x01 0x00 0x00 0x20 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0xE2

It is quite obvious that this is a SMC DECLINE message, which means that
the applications received SMC protocol message.
We found that this was caused by the following situations:

client			server
	   proposal
	------------->
	   accept
	<-------------
	   confirm
	------------->
wait confirm

	 failed llc confirm
	    x------
(after 2s)timeout
			wait rsp

wait decline

(after 1s) timeout
			(after 2s) timeout
	    decline
	-------------->
	    decline
	<--------------

As a result, a decline message was sent in the implementation, and this
message was read from TCP by the already-fallback connection.

This patch double the client timeout as 2x of the server value,
With this simple change, the Decline messages should never cross or
collide (during Confirm link timeout).

This issue requires an immediate solution, since the protocol updates
involve a more long-term solution.

Fixes: 0fb0b02bd6fd ("net/smc: adapt SMC client code to use the LLC flow")
Signed-off-by: D. Wythe <alibuda@...ux.alibaba.com>
---
 include/net/netns/smc.h |  2 ++
 net/smc/af_smc.c        |  3 ++-
 net/smc/smc_sysctl.c    | 12 ++++++++++++
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/include/net/netns/smc.h b/include/net/netns/smc.h
index 582212a..5198896 100644
--- a/include/net/netns/smc.h
+++ b/include/net/netns/smc.h
@@ -22,5 +22,7 @@ struct netns_smc {
 	int				sysctl_smcr_testlink_time;
 	int				sysctl_wmem;
 	int				sysctl_rmem;
+	/* server's Confirm Link timeout in seconds */
+	int				sysctl_smcr_srv_confirm_link_timeout;
 };
 #endif
diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index abd2667..b86ad30 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -1870,7 +1870,8 @@ static int smcr_serv_conf_first_link(struct smc_sock *smc)
 		return SMC_CLC_DECL_TIMEOUT_CL;
 
 	/* receive CONFIRM LINK response from client over the RoCE fabric */
-	qentry = smc_llc_wait(link->lgr, link, SMC_LLC_WAIT_TIME,
+	qentry = smc_llc_wait(link->lgr, link,
+			      sock_net(&smc->sk)->smc.sysctl_smcr_srv_confirm_link_timeout,
 			      SMC_LLC_CONFIRM_LINK);
 	if (!qentry) {
 		struct smc_clc_msg_decline dclc;
diff --git a/net/smc/smc_sysctl.c b/net/smc/smc_sysctl.c
index 5cbc18c..919f3f7 100644
--- a/net/smc/smc_sysctl.c
+++ b/net/smc/smc_sysctl.c
@@ -51,6 +51,13 @@
 		.proc_handler	= proc_dointvec_jiffies,
 	},
 	{
+		.procname	= "smcr_srv_confirm_link_timeout",
+		.data		= &init_net.smc.sysctl_smcr_srv_confirm_link_timeout,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_jiffies,
+	},
+	{
 		.procname	= "wmem",
 		.data		= &init_net.smc.sysctl_wmem,
 		.maxlen		= sizeof(int),
@@ -95,6 +102,11 @@ int __net_init smc_sysctl_net_init(struct net *net)
 	net->smc.sysctl_autocorking_size = SMC_AUTOCORKING_DEFAULT_SIZE;
 	net->smc.sysctl_smcr_buf_type = SMCR_PHYS_CONT_BUFS;
 	net->smc.sysctl_smcr_testlink_time = SMC_LLC_TESTLINK_DEFAULT_TIME;
+	/* Increasing the server's timeout by twice as much as the client's
+	 * timeout by default can temporarily avoid decline messages of
+	 * both side been crossed or collided.
+	 */
+	net->smc.sysctl_smcr_srv_confirm_link_timeout = 2 * SMC_LLC_WAIT_TIME;
 	WRITE_ONCE(net->smc.sysctl_wmem, net_smc_wmem_init);
 	WRITE_ONCE(net->smc.sysctl_rmem, net_smc_rmem_init);
 
-- 
1.8.3.1