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 <kerneljasonxing@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250317120314.41404-2-kerneljasonxing@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index 054561f8dcae77d4183f5b7e45f671ba8979390a..5c63ab928b97deb0bee6cf77b9b81985e0f46091 100644 (file)
--- 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 f8efe56bbccb17e92f84f6114a147bea7c303fa8..4450c384ef178e860bd76c23653e9ce9d7a7289b 100644 (file)
--- 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 92a2e79222ea551404ca6fc847327e5e7f617798..a126b3860e63caaa91dafd37631e285e7094aca8 100644 (file)
--- 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 fde56d28f586de27d7161565801d1c6962d7fbfe..a8a1370d642ebf1f504a2f66c504cbe601a8bd3c 100644 (file)
--- 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 @@ zerocopy_rcv_out:
        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;
        }