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Message-ID: <3f3080e2-cb2c-16f4-02b1-ca17394d2813@linux.alibaba.com> Date: Mon, 13 Nov 2023 10:50:03 +0800 From: "D. Wythe" <alibuda@...ux.alibaba.com> To: Wenjia Zhang <wenjia@...ux.ibm.com>, kgraul@...ux.ibm.com, jaka@...ux.ibm.com, wintera@...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 v1] net/smc: avoid data corruption caused by decline 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" <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> >>> --- >>> 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. >
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