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Message-ID: <1b7c95be-d3d9-53c3-3152-cd835314d37c@linux.ibm.com> Date: Thu, 16 Feb 2023 14:49:15 +0100 From: Wenjia Zhang <wenjia@...ux.ibm.com> To: "D. Wythe" <alibuda@...ux.alibaba.com>, kgraul@...ux.ibm.com, jaka@...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 v2] net/smc: fix application data exception On 16.02.23 07:39, D. Wythe wrote: > From: "D. Wythe" <alibuda@...ux.alibaba.com> > > There is a certain probability that following > exceptions will occur in the wrk benchmark test: > > Running 10s test @ http://11.213.45.6:80 > 8 threads and 64 connections > Thread Stats Avg Stdev Max +/- Stdev > Latency 3.72ms 13.94ms 245.33ms 94.17% > Req/Sec 1.96k 713.67 5.41k 75.16% > 155262 requests in 10.10s, 23.10MB read > Non-2xx or 3xx responses: 3 > > We will find that the error is HTTP 400 error, which is a serious > exception in our test, which means the application data was > corrupted. > > Consider the following scenarios: > > CPU0 CPU1 > > buf_desc->used = 0; > cmpxchg(buf_desc->used, 0, 1) > deal_with(buf_desc) > > memset(buf_desc->cpu_addr,0); > > This will cause the data received by a victim connection to be cleared, > thus triggering an HTTP 400 error in the server. > > This patch exchange the order between clear used and memset, add > barrier to ensure memory consistency. > > Fixes: 1c5526968e27 ("net/smc: Clear memory when release and reuse buffer") > Signed-off-by: D. Wythe <alibuda@...ux.alibaba.com> > --- > v2: rebase it with latest net tree. > Reviewed-by: Wenjia Zhang <wenjia@...ux.ibm.com> > net/smc/smc_core.c | 17 ++++++++--------- > 1 file changed, 8 insertions(+), 9 deletions(-) > > diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c > index c305d8d..c19d4b7 100644 > --- a/net/smc/smc_core.c > +++ b/net/smc/smc_core.c > @@ -1120,8 +1120,9 @@ static void smcr_buf_unuse(struct smc_buf_desc *buf_desc, bool is_rmb, > > smc_buf_free(lgr, is_rmb, buf_desc); > } else { > - buf_desc->used = 0; > - memset(buf_desc->cpu_addr, 0, buf_desc->len); > + /* memzero_explicit provides potential memory barrier semantics */ > + memzero_explicit(buf_desc->cpu_addr, buf_desc->len); > + WRITE_ONCE(buf_desc->used, 0); > } > } > > @@ -1132,19 +1133,17 @@ static void smc_buf_unuse(struct smc_connection *conn, > if (!lgr->is_smcd && conn->sndbuf_desc->is_vm) { > smcr_buf_unuse(conn->sndbuf_desc, false, lgr); > } else { > - conn->sndbuf_desc->used = 0; > - memset(conn->sndbuf_desc->cpu_addr, 0, > - conn->sndbuf_desc->len); > + memzero_explicit(conn->sndbuf_desc->cpu_addr, conn->sndbuf_desc->len); > + WRITE_ONCE(conn->sndbuf_desc->used, 0); > } > } > if (conn->rmb_desc) { > if (!lgr->is_smcd) { > smcr_buf_unuse(conn->rmb_desc, true, lgr); > } else { > - conn->rmb_desc->used = 0; > - memset(conn->rmb_desc->cpu_addr, 0, > - conn->rmb_desc->len + > - sizeof(struct smcd_cdc_msg)); > + memzero_explicit(conn->rmb_desc->cpu_addr, > + conn->rmb_desc->len + sizeof(struct smcd_cdc_msg)); > + WRITE_ONCE(conn->rmb_desc->used, 0); > } > } > }
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