From f38805c5d26fe4af97837c10d58074a7496638bf Mon Sep 17 00:00:00 2001 From: Jason Xing Date: Mon, 17 Mar 2025 20:03:13 +0800 Subject: [PATCH 1/2] tcp: support TCP_RTO_MIN_US for set/getsockopt use Support adjusting/reading RTO MIN for socket level by using set/getsockopt(). This new option has the same effect as TCP_BPF_RTO_MIN, which means it doesn't affect RTAX_RTO_MIN usage (by using ip route...). Considering that bpf option was implemented before this patch, so we need to use a standalone new option for pure tcp set/getsockopt() use. When the socket is created, its icsk_rto_min is set to the default value that is controlled by sysctl_tcp_rto_min_us. Then if application calls setsockopt() with TCP_RTO_MIN_US flag to pass a valid value, then icsk_rto_min will be overridden in jiffies unit. This patch adds WRITE_ONCE/READ_ONCE to avoid data-race around icsk_rto_min. Signed-off-by: Jason Xing Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20250317120314.41404-2-kerneljasonxing@gmail.com Signed-off-by: Jakub Kicinski --- Documentation/networking/ip-sysctl.rst | 4 ++-- include/net/tcp.h | 2 +- include/uapi/linux/tcp.h | 1 + net/ipv4/tcp.c | 13 ++++++++++++- 4 files changed, 16 insertions(+), 4 deletions(-) diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst index 054561f8dcae..5c63ab928b97 100644 --- a/Documentation/networking/ip-sysctl.rst +++ b/Documentation/networking/ip-sysctl.rst @@ -1229,8 +1229,8 @@ tcp_pingpong_thresh - INTEGER tcp_rto_min_us - INTEGER Minimal TCP retransmission timeout (in microseconds). Note that the rto_min route option has the highest precedence for configuring this - setting, followed by the TCP_BPF_RTO_MIN socket option, followed by - this tcp_rto_min_us sysctl. + setting, followed by the TCP_BPF_RTO_MIN and TCP_RTO_MIN_US socket + options, followed by this tcp_rto_min_us sysctl. The recommended practice is to use a value less or equal to 200000 microseconds. diff --git a/include/net/tcp.h b/include/net/tcp.h index f8efe56bbccb..4450c384ef17 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -844,7 +844,7 @@ u32 tcp_delack_max(const struct sock *sk); static inline u32 tcp_rto_min(const struct sock *sk) { const struct dst_entry *dst = __sk_dst_get(sk); - u32 rto_min = inet_csk(sk)->icsk_rto_min; + u32 rto_min = READ_ONCE(inet_csk(sk)->icsk_rto_min); if (dst && dst_metric_locked(dst, RTAX_RTO_MIN)) rto_min = dst_metric_rtt(dst, RTAX_RTO_MIN); diff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h index 92a2e79222ea..a126b3860e63 100644 --- a/include/uapi/linux/tcp.h +++ b/include/uapi/linux/tcp.h @@ -140,6 +140,7 @@ enum { #define TCP_IS_MPTCP 43 /* Is MPTCP being used? */ #define TCP_RTO_MAX_MS 44 /* max rto time in ms */ +#define TCP_RTO_MIN_US 45 /* min rto time in us */ #define TCP_REPAIR_ON 1 #define TCP_REPAIR_OFF 0 diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index fde56d28f586..a8a1370d642e 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -3352,7 +3352,7 @@ int tcp_disconnect(struct sock *sk, int flags) icsk->icsk_probes_out = 0; icsk->icsk_probes_tstamp = 0; icsk->icsk_rto = TCP_TIMEOUT_INIT; - icsk->icsk_rto_min = TCP_RTO_MIN; + WRITE_ONCE(icsk->icsk_rto_min, TCP_RTO_MIN); icsk->icsk_delack_max = TCP_DELACK_MAX; tp->snd_ssthresh = TCP_INFINITE_SSTHRESH; tcp_snd_cwnd_set(tp, TCP_INIT_CWND); @@ -3833,6 +3833,14 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname, return -EINVAL; WRITE_ONCE(inet_csk(sk)->icsk_rto_max, msecs_to_jiffies(val)); return 0; + case TCP_RTO_MIN_US: { + int rto_min = usecs_to_jiffies(val); + + if (rto_min > TCP_RTO_MIN || rto_min < TCP_TIMEOUT_MIN) + return -EINVAL; + WRITE_ONCE(inet_csk(sk)->icsk_rto_min, rto_min); + return 0; + } } sockopt_lock_sock(sk); @@ -4672,6 +4680,9 @@ int do_tcp_getsockopt(struct sock *sk, int level, case TCP_RTO_MAX_MS: val = jiffies_to_msecs(tcp_rto_max(sk)); break; + case TCP_RTO_MIN_US: + val = jiffies_to_usecs(READ_ONCE(inet_csk(sk)->icsk_rto_min)); + break; default: return -ENOPROTOOPT; } From 9552f90835ef3552d0af327e48dc360717777d62 Mon Sep 17 00:00:00 2001 From: Jason Xing Date: Mon, 17 Mar 2025 20:03:14 +0800 Subject: [PATCH 2/2] tcp: support TCP_DELACK_MAX_US for set/getsockopt use Support adjusting/reading delayed ack max for socket level by using set/getsockopt(). This option aligns with TCP_BPF_DELACK_MAX usage. Considering that bpf option was implemented before this patch, so we need to use a standalone new option for pure tcp set/getsockopt() use. Add WRITE_ONCE/READ_ONCE() to prevent data-race if setsockopt() happens to write one value to icsk_delack_max while icsk_delack_max is being read. Signed-off-by: Jason Xing Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20250317120314.41404-3-kerneljasonxing@gmail.com Signed-off-by: Jakub Kicinski --- include/uapi/linux/tcp.h | 1 + net/ipv4/tcp.c | 13 ++++++++++++- net/ipv4/tcp_output.c | 2 +- 3 files changed, 14 insertions(+), 2 deletions(-) diff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h index a126b3860e63..dc8fdc80e16b 100644 --- a/include/uapi/linux/tcp.h +++ b/include/uapi/linux/tcp.h @@ -141,6 +141,7 @@ enum { #define TCP_IS_MPTCP 43 /* Is MPTCP being used? */ #define TCP_RTO_MAX_MS 44 /* max rto time in ms */ #define TCP_RTO_MIN_US 45 /* min rto time in us */ +#define TCP_DELACK_MAX_US 46 /* max delayed ack time in us */ #define TCP_REPAIR_ON 1 #define TCP_REPAIR_OFF 0 diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index a8a1370d642e..6edc441b3702 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -3353,7 +3353,7 @@ int tcp_disconnect(struct sock *sk, int flags) icsk->icsk_probes_tstamp = 0; icsk->icsk_rto = TCP_TIMEOUT_INIT; WRITE_ONCE(icsk->icsk_rto_min, TCP_RTO_MIN); - icsk->icsk_delack_max = TCP_DELACK_MAX; + WRITE_ONCE(icsk->icsk_delack_max, TCP_DELACK_MAX); tp->snd_ssthresh = TCP_INFINITE_SSTHRESH; tcp_snd_cwnd_set(tp, TCP_INIT_CWND); tp->snd_cwnd_cnt = 0; @@ -3841,6 +3841,14 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname, WRITE_ONCE(inet_csk(sk)->icsk_rto_min, rto_min); return 0; } + case TCP_DELACK_MAX_US: { + int delack_max = usecs_to_jiffies(val); + + if (delack_max > TCP_DELACK_MAX || delack_max < TCP_TIMEOUT_MIN) + return -EINVAL; + WRITE_ONCE(inet_csk(sk)->icsk_delack_max, delack_max); + return 0; + } } sockopt_lock_sock(sk); @@ -4683,6 +4691,9 @@ int do_tcp_getsockopt(struct sock *sk, int level, case TCP_RTO_MIN_US: val = jiffies_to_usecs(READ_ONCE(inet_csk(sk)->icsk_rto_min)); break; + case TCP_DELACK_MAX_US: + val = jiffies_to_usecs(READ_ONCE(inet_csk(sk)->icsk_delack_max)); + break; default: return -ENOPROTOOPT; } diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index e0a4e5432399..9a6061017114 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -4179,7 +4179,7 @@ u32 tcp_delack_max(const struct sock *sk) { u32 delack_from_rto_min = max(tcp_rto_min(sk), 2) - 1; - return min(inet_csk(sk)->icsk_delack_max, delack_from_rto_min); + return min(READ_ONCE(inet_csk(sk)->icsk_delack_max), delack_from_rto_min); } /* Send out a delayed ack, the caller does the policy checking