| Message ID | 1676529545-32741-1-git-send-email-alibuda@linux.alibaba.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | [net,v2] net/smc: fix application data exception | expand |
On 16.02.23 07:39, D. Wythe wrote: > From: "D. Wythe" <alibuda@linux.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@linux.alibaba.com> > --- > v2: rebase it with latest net tree. > Reviewed-by: Wenjia Zhang <wenjia@linux.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); > } > } > }
On Thu, Feb 16, 2023 at 02:39:05PM +0800, D. Wythe wrote: > From: "D. Wythe" <alibuda@linux.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@linux.alibaba.com> > --- > 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); This looks odd to me. memzero_explicit() is only sort of a compiler barrier, since it is a function call, but not a real memory barrier. You may want to check Documentation/memory-barriers.txt and Documentation/atomic_t.txt. To me the proper solution looks like buf_desc->used should be converted to an atomic_t, and then you could do: memset(buf_desc->cpu_addr, 0, buf_desc->len); smp_mb__before_atomic(); atomic_set(&buf_desc->used, 0); and in a similar way use atomic_cmpxchg() instead of the now used cmpxchg() for the part that sets buf_desc->used to 1. Adding experts to cc, since s390 has such strong memory ordering semantics that you can basically do whatever you want without breaking anything. So I don't consider myself an expert here at all. :) But given that this is common code, let's make sure this is really correct.
On 3/1/23 2:37 AM, Heiko Carstens wrote: > On Thu, Feb 16, 2023 at 02:39:05PM +0800, D. Wythe wrote: >> From: "D. Wythe" <alibuda@linux.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@linux.alibaba.com> >> --- >> 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); > > This looks odd to me. memzero_explicit() is only sort of a compiler > barrier, since it is a function call, but not a real memory barrier. Hi Heiko, Thanks for you point out, the semantics of memzero_explicit is exactly what you said. But my original intention is just wants to ensure the order relationship between memset and the assignment. I'm not really sure whether a CPU memory barrier is needed here. > You may want to check Documentation/memory-barriers.txt and > Documentation/atomic_t.txt. > > To me the proper solution looks like buf_desc->used should be converted to > an atomic_t, and then you could do: > > memset(buf_desc->cpu_addr, 0, buf_desc->len); > smp_mb__before_atomic(); > atomic_set(&buf_desc->used, 0); Anyhow, your solution is definitely correct, because that CPU memory barrier (smp_mb__before_atomic) implies the compiler barrier. > and in a similar way use atomic_cmpxchg() instead of the now used cmpxchg() > for the part that sets buf_desc->used to 1. > > Adding experts to cc, since s390 has such strong memory ordering semantics > that you can basically do whatever you want without breaking anything. So I > don't consider myself an expert here at all. :) > > But given that this is common code, let's make sure this is really correct Thank you for your comments again. :-), I am looking up some more information, and I believe I can reply to you soon. best wishes, D. Wythe
On 3/1/23 2:37 AM, Heiko Carstens wrote: > On Thu, Feb 16, 2023 at 02:39:05PM +0800, D. Wythe wrote: >> From: "D. Wythe" <alibuda@linux.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@linux.alibaba.com> >> --- >> 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); > This looks odd to me. memzero_explicit() is only sort of a compiler > barrier, since it is a function call, but not a real memory barrier. > > You may want to check Documentation/memory-barriers.txt and > Documentation/atomic_t.txt. > > To me the proper solution looks like buf_desc->used should be converted to > an atomic_t, and then you could do: > > memset(buf_desc->cpu_addr, 0, buf_desc->len); > smp_mb__before_atomic(); > atomic_set(&buf_desc->used, 0); > > and in a similar way use atomic_cmpxchg() instead of the now used cmpxchg() > for the part that sets buf_desc->used to 1. > > Adding experts to cc, since s390 has such strong memory ordering semantics > that you can basically do whatever you want without breaking anything. So I > don't consider myself an expert here at all. :) > > But given that this is common code, let's make sure this is really correct. Hi Heiko, I realize that you are completely right, and I will repair this problem according to your ideas. Thank you very much!!! Best wishes. D. Wythe
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); } } }