From: Daniel Borkmann <dan...@iogearbox.net>
Currently, the following case doesn't use DCTCP, even if it should:
A responder has f.e. Cubic as system wide default, but for a specific
route to the initiating host, DCTCP is being set in RTAX_CC_ALGO. The
initiating host then uses DCTCP as congestion control, but since the
initiator sets ECT(0), tcp_ecn_create_request() doesn't set ecn_ok,
and we have to fall back to Reno after 3WHS completes.
We were thinking on how to solve this in a minimal, non-intrusive
way without bloating tcp_ecn_create_request() needlessly: lets cache
the CA ecn option flag in RTAX_FEATURES. In other words, when ECT(0)
is set on the SYN packet, set ecn_ok=1 iff route RTAX_FEATURES
contains RTAX_FEATURE_ECN_CA. This allows to only do a single metric
feature lookup inside tcp_ecn_create_request().
Joint work with Florian Westphal.
Signed-off-by: Daniel Borkmann <dan...@iogearbox.net>
Signed-off-by: Florian Westphal <f...@strlen.de>
---
include/net/tcp.h | 2 +-
include/uapi/linux/rtnetlink.h | 11 +++++++----
net/core/rtnetlink.c | 4 ++++
net/ipv4/fib_semantics.c | 9 ++++++++-
net/ipv4/tcp_cong.c | 9 ++++++---
net/ipv4/tcp_input.c | 7 +++++--
net/ipv6/route.c | 11 +++++++++--
7 files changed, 40 insertions(+), 13 deletions(-)
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 4a7b039..0cab28c 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -888,7 +888,7 @@ void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32
acked);
extern struct tcp_congestion_ops tcp_reno;
struct tcp_congestion_ops *tcp_ca_find_key(u32 key);
-u32 tcp_ca_get_key_by_name(const char *name);
+u32 tcp_ca_get_key_by_name(const char *name, bool *ecn_ca);
#ifdef CONFIG_INET
char *tcp_ca_get_name_by_key(u32 key, char *buffer);
#else
diff --git a/include/uapi/linux/rtnetlink.h b/include/uapi/linux/rtnetlink.h
index 0d3d3cc..a5eb242 100644
--- a/include/uapi/linux/rtnetlink.h
+++ b/include/uapi/linux/rtnetlink.h
@@ -418,10 +418,13 @@ enum {
#define RTAX_MAX (__RTAX_MAX - 1)
-#define RTAX_FEATURE_ECN 0x00000001
-#define RTAX_FEATURE_SACK 0x00000002
-#define RTAX_FEATURE_TIMESTAMP 0x00000004
-#define RTAX_FEATURE_ALLFRAG 0x00000008
+#define RTAX_FEATURE_ECN (1 << 0)
+#define RTAX_FEATURE_SACK (1 << 1)
+#define RTAX_FEATURE_TIMESTAMP (1 << 2)
+#define RTAX_FEATURE_ALLFRAG (1 << 3)
+#define RTAX_FEATURE_ECN_CA (1 << 4)
+
+#define RTAX_FEATURE_MASK_ECN (RTAX_FEATURE_ECN | RTAX_FEATURE_ECN_CA)
struct rta_session {
__u8 proto;
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index 788ceed..12a9b5a 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -678,6 +678,10 @@ int rtnetlink_put_metrics(struct sk_buff *skb, u32
*metrics)
continue;
if (nla_put_string(skb, i + 1, name))
goto nla_put_failure;
+ } else if (i == RTAX_FEATURES - 1) {
+ u32 feat = metrics[i] & ~RTAX_FEATURE_ECN_CA;
+ if (nla_put_u32(skb, i + 1, feat))
+ goto nla_put_failure;
} else {
if (nla_put_u32(skb, i + 1, metrics[i]))
goto nla_put_failure;
diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index 88afbae..d7ecc92 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -879,6 +879,7 @@ static bool fib_valid_prefsrc(struct fib_config *cfg,
__be32 fib_prefsrc)
static int
fib_convert_metrics(struct fib_info *fi, const struct fib_config *cfg)
{
+ bool ecn_ca = false;
struct nlattr *nla;
int remaining;
@@ -898,7 +899,7 @@ fib_convert_metrics(struct fib_info *fi, const struct
fib_config *cfg)
char tmp[TCP_CA_NAME_MAX];
nla_strlcpy(tmp, nla, sizeof(tmp));
- val = tcp_ca_get_key_by_name(tmp);
+ val = tcp_ca_get_key_by_name(tmp, &ecn_ca);
if (val == TCP_CA_UNSPEC)
return -EINVAL;
} else {
@@ -908,9 +909,15 @@ fib_convert_metrics(struct fib_info *fi, const struct
fib_config *cfg)
val = 65535 - 40;
if (type == RTAX_MTU && val > 65535 - 15)
val = 65535 - 15;
+ if (type == RTAX_FEATURES)
+ val &= ~RTAX_FEATURE_ECN_CA;
+
fi->fib_metrics[type - 1] = val;
}
+ if (ecn_ca)
+ fi->fib_metrics[RTAX_FEATURES - 1] |= RTAX_FEATURE_ECN_CA;
+
return 0;
}
diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index a2ed23c..93c4dc3 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -114,16 +114,19 @@ void tcp_unregister_congestion_control(struct
tcp_congestion_ops *ca)
}
EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
-u32 tcp_ca_get_key_by_name(const char *name)
+u32 tcp_ca_get_key_by_name(const char *name, bool *ecn_ca)
{
const struct tcp_congestion_ops *ca;
- u32 key;
+ u32 key = TCP_CA_UNSPEC;
might_sleep();
rcu_read_lock();
ca = __tcp_ca_find_autoload(name);
- key = ca ? ca->key : TCP_CA_UNSPEC;
+ if (ca) {
+ key = ca->key;
+ *ecn_ca = ca->flags & TCP_CONG_NEEDS_ECN;
+ }
rcu_read_unlock();
return key;
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index dc08e23..39f0375 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6003,14 +6003,17 @@ static void tcp_ecn_create_request(struct request_sock
*req,
const struct net *net = sock_net(listen_sk);
bool th_ecn = th->ece && th->cwr;
bool ect, ecn_ok;
+ u32 ecn_ok_dst;
if (!th_ecn)
return;
ect = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield);
- ecn_ok = net->ipv4.sysctl_tcp_ecn || dst_feature(dst, RTAX_FEATURE_ECN);
+ ecn_ok_dst = dst_feature(dst, RTAX_FEATURE_MASK_ECN);
+ ecn_ok = net->ipv4.sysctl_tcp_ecn || ecn_ok_dst;
- if ((!ect && ecn_ok) || tcp_ca_needs_ecn(listen_sk))
+ if ((!ect && ecn_ok) || tcp_ca_needs_ecn(listen_sk) ||
+ (ecn_ok_dst & RTAX_FEATURE_ECN_CA))
inet_rsk(req)->ecn_ok = 1;
}
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 56b2e71..f1d3de4 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1698,6 +1698,7 @@ out:
static int ip6_convert_metrics(struct mx6_config *mxc,
const struct fib6_config *cfg)
{
+ bool ecn_ca = false;
struct nlattr *nla;
int remaining;
u32 *mp;
@@ -1722,19 +1723,25 @@ static int ip6_convert_metrics(struct mx6_config *mxc,
char tmp[TCP_CA_NAME_MAX];
nla_strlcpy(tmp, nla, sizeof(tmp));
- val = tcp_ca_get_key_by_name(tmp);
+ val = tcp_ca_get_key_by_name(tmp, &ecn_ca);
if (val == TCP_CA_UNSPEC)
goto err;
} else {
val = nla_get_u32(nla);
}
+ if (type == RTAX_FEATURES)
+ val &= ~RTAX_FEATURE_ECN_CA;
mp[type - 1] = val;
__set_bit(type - 1, mxc->mx_valid);
}
- mxc->mx = mp;
+ if (ecn_ca) {
+ __set_bit(RTAX_FEATURES - 1, mxc->mx_valid);
+ mp[RTAX_FEATURES - 1] |= RTAX_FEATURE_ECN_CA;
+ }
+ mxc->mx = mp;
return 0;
err:
kfree(mp);
--
2.0.5
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