From: "D. Wythe" <alibuda@xxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxx> --- v2: rebase it with latest net tree. 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); } } } -- 1.8.3.1
