tcp: Fix data-races around sysctl_tcp_no_ssthresh_metrics_save.

While reading sysctl_tcp_no_ssthresh_metrics_save, it can be changed
concurrently.  Thus, we need to add READ_ONCE() to its readers.

Fixes: cef2872422a9 ("net-tcp: Disable TCP ssthresh metrics cache by default")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp_metrics.c b/net/ipv4/tcp_metrics.c
index 9dcc418a26f298a1f79196f2cabe5ce430837ca2..d58e672be31c764805ca6ad120459eb2d86b4d87 100644 (file)
--- a/net/ipv4/tcp_metrics.c
+++ b/net/ipv4/tcp_metrics.c
@@ -385,7 +385,7 @@ void tcp_update_metrics(struct sock *sk)
 
        if (tcp_in_initial_slowstart(tp)) {
                /* Slow start still did not finish. */
-               if (!net->ipv4.sysctl_tcp_no_ssthresh_metrics_save &&
+               if (!READ_ONCE(net->ipv4.sysctl_tcp_no_ssthresh_metrics_save) &&
                    !tcp_metric_locked(tm, TCP_METRIC_SSTHRESH)) {
                        val = tcp_metric_get(tm, TCP_METRIC_SSTHRESH);
                        if (val && (tcp_snd_cwnd(tp) >> 1) > val)
@@ -401,7 +401,7 @@ void tcp_update_metrics(struct sock *sk)
        } else if (!tcp_in_slow_start(tp) &&
                   icsk->icsk_ca_state == TCP_CA_Open) {
                /* Cong. avoidance phase, cwnd is reliable. */
-               if (!net->ipv4.sysctl_tcp_no_ssthresh_metrics_save &&
+               if (!READ_ONCE(net->ipv4.sysctl_tcp_no_ssthresh_metrics_save) &&
                    !tcp_metric_locked(tm, TCP_METRIC_SSTHRESH))
                        tcp_metric_set(tm, TCP_METRIC_SSTHRESH,
                                       max(tcp_snd_cwnd(tp) >> 1, tp->snd_ssthresh));
@@ -418,7 +418,7 @@ void tcp_update_metrics(struct sock *sk)
                        tcp_metric_set(tm, TCP_METRIC_CWND,
                                       (val + tp->snd_ssthresh) >> 1);
                }
-               if (!net->ipv4.sysctl_tcp_no_ssthresh_metrics_save &&
+               if (!READ_ONCE(net->ipv4.sysctl_tcp_no_ssthresh_metrics_save) &&
                    !tcp_metric_locked(tm, TCP_METRIC_SSTHRESH)) {
                        val = tcp_metric_get(tm, TCP_METRIC_SSTHRESH);
                        if (val && tp->snd_ssthresh > val)
@@ -463,7 +463,7 @@ void tcp_init_metrics(struct sock *sk)
        if (tcp_metric_locked(tm, TCP_METRIC_CWND))
                tp->snd_cwnd_clamp = tcp_metric_get(tm, TCP_METRIC_CWND);
 
-       val = net->ipv4.sysctl_tcp_no_ssthresh_metrics_save ?
+       val = READ_ONCE(net->ipv4.sysctl_tcp_no_ssthresh_metrics_save) ?
              0 : tcp_metric_get(tm, TCP_METRIC_SSTHRESH);
        if (val) {
                tp->snd_ssthresh = val;