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Message-ID: <17abf559-ec8b-47e9-b4e4-59adfbc6943b@linux.ibm.com> Date: Wed, 15 Nov 2023 15:06:21 +0100 From: Wenjia Zhang <wenjia@...ux.ibm.com> To: dust.li@...ux.alibaba.com, "D. Wythe" <alibuda@...ux.alibaba.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 13.11.23 04:44, Dust Li wrote: > On Wed, Nov 08, 2023 at 05:48:29PM +0800, 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); > > It may be difficult for people to understand why LLC_WAIT_TIME is > different, especially without any comments explaining its purpose. > People are required to use git to find the reason, which I believe is > not conducive to easy maintenance. > > Best regards, > Dust > > Good point! @D.Wythe, could you please try to add a simple commet to explain it? Thanks, Wenjia > >> if (!qentry) { >> struct smc_clc_msg_decline dclc; >> -- >> 1.8.3.1
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