* [PATCH net-next 1/2] tcp: annotate data-races around tp->rx_opt.user_mss
2025-08-21 14:18 [PATCH net-next 0/2] tcp: user_mss and TCP_MAXSEG series Eric Dumazet
@ 2025-08-21 14:19 ` Eric Dumazet
2025-08-21 14:28 ` Neal Cardwell
2025-08-21 14:19 ` [PATCH net-next 2/2] tcp: lockless TCP_MAXSEG option Eric Dumazet
2025-08-22 23:40 ` [PATCH net-next 0/2] tcp: user_mss and TCP_MAXSEG series patchwork-bot+netdevbpf
2 siblings, 1 reply; 6+ messages in thread
From: Eric Dumazet @ 2025-08-21 14:19 UTC (permalink / raw)
To: David S . Miller, Jakub Kicinski, Paolo Abeni, Neal Cardwell
Cc: Simon Horman, Kuniyuki Iwashima, Willem de Bruijn, netdev,
eric.dumazet, Eric Dumazet
This field is already read locklessly for listeners,
next patch will make setsockopt(TCP_MAXSEG) lockless.
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
.../net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c | 6 ++++--
.../net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.h | 2 +-
net/ipv4/tcp.c | 8 +++++---
net/ipv4/tcp_input.c | 8 ++++----
net/ipv4/tcp_output.c | 6 ++++--
5 files changed, 18 insertions(+), 12 deletions(-)
diff --git a/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c b/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c
index 2e7c2691a1933e5c8d9dc71ec99a5d92970ad7cd..000116e47e38d90802c5dd676c0659fab19bcff3 100644
--- a/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c
+++ b/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c
@@ -951,6 +951,7 @@ static unsigned int chtls_select_mss(const struct chtls_sock *csk,
struct tcp_sock *tp;
unsigned int mss;
struct sock *sk;
+ u16 user_mss;
mss = ntohs(req->tcpopt.mss);
sk = csk->sk;
@@ -969,8 +970,9 @@ static unsigned int chtls_select_mss(const struct chtls_sock *csk,
tcpoptsz += round_up(TCPOLEN_TIMESTAMP, 4);
tp->advmss = dst_metric_advmss(dst);
- if (USER_MSS(tp) && tp->advmss > USER_MSS(tp))
- tp->advmss = USER_MSS(tp);
+ user_mss = USER_MSS(tp);
+ if (user_mss && tp->advmss > user_mss)
+ tp->advmss = user_mss;
if (tp->advmss > pmtu - iphdrsz)
tp->advmss = pmtu - iphdrsz;
if (mss && tp->advmss > mss)
diff --git a/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.h b/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.h
index 2285cf2df251db9ec84d305d5ffa012279f6c43f..667effc2a23cb78901d65da2712a7e8a66ec81b4 100644
--- a/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.h
+++ b/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.h
@@ -90,7 +90,7 @@ struct deferred_skb_cb {
#define SND_WSCALE(tp) ((tp)->rx_opt.snd_wscale)
#define RCV_WSCALE(tp) ((tp)->rx_opt.rcv_wscale)
-#define USER_MSS(tp) ((tp)->rx_opt.user_mss)
+#define USER_MSS(tp) (READ_ONCE((tp)->rx_opt.user_mss))
#define TS_RECENT_STAMP(tp) ((tp)->rx_opt.ts_recent_stamp)
#define WSCALE_OK(tp) ((tp)->rx_opt.wscale_ok)
#define TSTAMP_OK(tp) ((tp)->rx_opt.tstamp_ok)
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 71a956fbfc5533224ee00e792de2cfdccd4d40aa..a12d81e01b3f2fb964227881c2f779741cc06e58 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3760,7 +3760,7 @@ int tcp_sock_set_maxseg(struct sock *sk, int val)
if (val && (val < TCP_MIN_MSS || val > MAX_TCP_WINDOW))
return -EINVAL;
- tcp_sk(sk)->rx_opt.user_mss = val;
+ WRITE_ONCE(tcp_sk(sk)->rx_opt.user_mss, val);
return 0;
}
@@ -4383,6 +4383,7 @@ int do_tcp_getsockopt(struct sock *sk, int level,
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
struct net *net = sock_net(sk);
+ int user_mss;
int val, len;
if (copy_from_sockptr(&len, optlen, sizeof(int)))
@@ -4396,9 +4397,10 @@ int do_tcp_getsockopt(struct sock *sk, int level,
switch (optname) {
case TCP_MAXSEG:
val = tp->mss_cache;
- if (tp->rx_opt.user_mss &&
+ user_mss = READ_ONCE(tp->rx_opt.user_mss);
+ if (user_mss &&
((1 << sk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)))
- val = tp->rx_opt.user_mss;
+ val = user_mss;
if (tp->repair)
val = tp->rx_opt.mss_clamp;
break;
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 71b76e98371a667b6e8263b32c242363672d7c5a..7b537978dfe6b436c723815f1ce64f05f9c1ae61 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6297,7 +6297,7 @@ static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
u16 mss = tp->rx_opt.mss_clamp, try_exp = 0;
bool syn_drop = false;
- if (mss == tp->rx_opt.user_mss) {
+ if (mss == READ_ONCE(tp->rx_opt.user_mss)) {
struct tcp_options_received opt;
/* Get original SYNACK MSS value if user MSS sets mss_clamp */
@@ -7117,7 +7117,7 @@ u16 tcp_get_syncookie_mss(struct request_sock_ops *rsk_ops,
return 0;
}
- mss = tcp_parse_mss_option(th, tp->rx_opt.user_mss);
+ mss = tcp_parse_mss_option(th, READ_ONCE(tp->rx_opt.user_mss));
if (!mss)
mss = af_ops->mss_clamp;
@@ -7131,7 +7131,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
{
struct tcp_fastopen_cookie foc = { .len = -1 };
struct tcp_options_received tmp_opt;
- struct tcp_sock *tp = tcp_sk(sk);
+ const struct tcp_sock *tp = tcp_sk(sk);
struct net *net = sock_net(sk);
struct sock *fastopen_sk = NULL;
struct request_sock *req;
@@ -7182,7 +7182,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
tcp_clear_options(&tmp_opt);
tmp_opt.mss_clamp = af_ops->mss_clamp;
- tmp_opt.user_mss = tp->rx_opt.user_mss;
+ tmp_opt.user_mss = READ_ONCE(tp->rx_opt.user_mss);
tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0,
want_cookie ? NULL : &foc);
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index dfbac0876d96ee6b556fff5b6c9ec8fe2e04aa05..86892c8672ed49a49b85530b648d695ed171a3c8 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -3890,6 +3890,7 @@ static void tcp_connect_init(struct sock *sk)
const struct dst_entry *dst = __sk_dst_get(sk);
struct tcp_sock *tp = tcp_sk(sk);
__u8 rcv_wscale;
+ u16 user_mss;
u32 rcv_wnd;
/* We'll fix this up when we get a response from the other end.
@@ -3902,8 +3903,9 @@ static void tcp_connect_init(struct sock *sk)
tcp_ao_connect_init(sk);
/* If user gave his TCP_MAXSEG, record it to clamp */
- if (tp->rx_opt.user_mss)
- tp->rx_opt.mss_clamp = tp->rx_opt.user_mss;
+ user_mss = READ_ONCE(tp->rx_opt.user_mss);
+ if (user_mss)
+ tp->rx_opt.mss_clamp = user_mss;
tp->max_window = 0;
tcp_mtup_init(sk);
tcp_sync_mss(sk, dst_mtu(dst));
--
2.51.0.rc1.193.gad69d77794-goog
^ permalink raw reply related [flat|nested] 6+ messages in thread* [PATCH net-next 2/2] tcp: lockless TCP_MAXSEG option
2025-08-21 14:18 [PATCH net-next 0/2] tcp: user_mss and TCP_MAXSEG series Eric Dumazet
2025-08-21 14:19 ` [PATCH net-next 1/2] tcp: annotate data-races around tp->rx_opt.user_mss Eric Dumazet
@ 2025-08-21 14:19 ` Eric Dumazet
2025-08-21 14:28 ` Neal Cardwell
2025-08-22 23:40 ` [PATCH net-next 0/2] tcp: user_mss and TCP_MAXSEG series patchwork-bot+netdevbpf
2 siblings, 1 reply; 6+ messages in thread
From: Eric Dumazet @ 2025-08-21 14:19 UTC (permalink / raw)
To: David S . Miller, Jakub Kicinski, Paolo Abeni, Neal Cardwell
Cc: Simon Horman, Kuniyuki Iwashima, Willem de Bruijn, netdev,
eric.dumazet, Eric Dumazet
setsockopt(TCP_MAXSEG) writes over a field that does not need
socket lock protection anymore.
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
net/ipv4/tcp.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index a12d81e01b3f2fb964227881c2f779741cc06e58..99232903b03c99d263cce59314fd369cfd33af6f 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3890,15 +3890,13 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname,
WRITE_ONCE(inet_csk(sk)->icsk_delack_max, delack_max);
return 0;
}
+ case TCP_MAXSEG:
+ return tcp_sock_set_maxseg(sk, val);
}
sockopt_lock_sock(sk);
switch (optname) {
- case TCP_MAXSEG:
- err = tcp_sock_set_maxseg(sk, val);
- break;
-
case TCP_NODELAY:
__tcp_sock_set_nodelay(sk, val);
break;
--
2.51.0.rc1.193.gad69d77794-goog
^ permalink raw reply related [flat|nested] 6+ messages in thread