From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7D728C4167D for ; Mon, 13 Nov 2023 02:50:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232923AbjKMCuN (ORCPT ); Sun, 12 Nov 2023 21:50:13 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56304 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230053AbjKMCuN (ORCPT ); Sun, 12 Nov 2023 21:50:13 -0500 Received: from out30-112.freemail.mail.aliyun.com (out30-112.freemail.mail.aliyun.com [115.124.30.112]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0828610E; Sun, 12 Nov 2023 18:50:08 -0800 (PST) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R141e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045176;MF=alibuda@linux.alibaba.com;NM=1;PH=DS;RN=9;SR=0;TI=SMTPD_---0VwBTFXs_1699843805; Received: from 30.221.147.142(mailfrom:alibuda@linux.alibaba.com fp:SMTPD_---0VwBTFXs_1699843805) by smtp.aliyun-inc.com; Mon, 13 Nov 2023 10:50:06 +0800 Message-ID: <3f3080e2-cb2c-16f4-02b1-ca17394d2813@linux.alibaba.com> Date: Mon, 13 Nov 2023 10:50:03 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.15.1 Subject: Re: [PATCH net v1] net/smc: avoid data corruption caused by decline Content-Language: en-US From: "D. Wythe" To: Wenjia Zhang , kgraul@linux.ibm.com, jaka@linux.ibm.com, wintera@linux.ibm.com Cc: kuba@kernel.org, davem@davemloft.net, netdev@vger.kernel.org, linux-s390@vger.kernel.org, linux-rdma@vger.kernel.org References: <1699436909-22767-1-git-send-email-alibuda@linux.alibaba.com> <05c29431-c941-45d1-8e14-0527accc3993@linux.ibm.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org On 11/10/23 10:51 AM, D. Wythe wrote: > > > On 11/8/23 9:00 PM, Wenjia Zhang wrote: >> >> >> On 08.11.23 10:48, D. Wythe wrote: >>> From: "D. Wythe" >>> >>> 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 >>> --- >>>   net/smc/af_smc.c | 2 +- >>>   1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c >>> index abd2667..5b91f55 100644 >>> --- a/net/smc/af_smc.c >>> +++ b/net/smc/af_smc.c >>> @@ -599,7 +599,7 @@ static int smcr_clnt_conf_first_link(struct >>> smc_sock *smc) >>>       int rc; >>>         /* receive CONFIRM LINK request from server over RoCE fabric */ >>> -    qentry = smc_llc_wait(link->lgr, NULL, SMC_LLC_WAIT_TIME, >>> +    qentry = smc_llc_wait(link->lgr, NULL, 2 * SMC_LLC_WAIT_TIME, >>>                     SMC_LLC_CONFIRM_LINK); >>>       if (!qentry) { >>>           struct smc_clc_msg_decline dclc; >> I'm wondering if the double time (if sufficient) of timeout could be >> for waiting for CLC_DECLINE on the client's side. i.e. >> > > It depends. We can indeed introduce a sysctl to allow server to > manager their Confirm Link timeout, > but if there will be protocol updates, this introduction will no > longer be necessary, and we will > have to maintain it continuously. > > I believe the core of the solution is to ensure that decline messages > never cross or collide. Increasing > the client's timeout by twice as much as the server's timeout can > temporarily solve this problem. > If Jerry's proposed protocol updates are too complex or if there won't > be any future protocol updates, > it's still not late to let server manager their Confirm Link timeout then. > > Best wishes, > D. Wythe > FYI: It seems that my email was not successfully delivered due to some reasons. Sorry for that. D. Wythe >> diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c >> index 35ddebae8894..9b1feef1013d 100644 >> --- a/net/smc/af_smc.c >> +++ b/net/smc/af_smc.c >> @@ -605,7 +605,7 @@ static int smcr_clnt_conf_first_link(struct >> smc_sock *smc) >>                 struct smc_clc_msg_decline dclc; >> >>                 rc = smc_clc_wait_msg(smc, &dclc, sizeof(dclc), >> -                                     SMC_CLC_DECLINE, >> CLC_WAIT_TIME_SHORT); >> +                                     SMC_CLC_DECLINE, 2 * >> CLC_WAIT_TIME_SHORT); >>                 return rc == -EAGAIN ? SMC_CLC_DECL_TIMEOUT_CL : rc; >>         } >>         smc_llc_save_peer_uid(qentry); >> >> Because the purpose is to let the server have the control to deline. >