[PATCH net-next 2/2] tcp: fix showing wrong rtomin in snmp file when setting sysctl_tcp_rto_min_us

[Jason Xing <kerneljasonxing@gmail.com>]

From: Jason Xing <kernelxing@tencent.com>

A few days ago, sysctl_tcp_rto_min_us has been introduced to allow user to
tune the rto min value per netns. But the RtoMin field in /proc/net/snmp
should have been adjusted accordingly. Or else, it will show 200 which is
TCP_RTO_MIN.

This patch can show the correct value even when user sets though using both
'ip route' and 'sysctl -w'. The priority from high to low like what
tcp_rto_min() shows to us is:
1) ip route option rto_min
2) icsk->icsk_rto_min

Fixes: f086edef71be ("tcp: add sysctl_tcp_rto_min_us")
Signed-off-by: Jason Xing <kernelxing@tencent.com>
---
 net/ipv4/proc.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index ce387081a3c9..4aeef3118442 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -409,6 +409,19 @@ static int snmp_seq_show_ipstats(struct seq_file *seq, void *v)
 	return 0;
 }
 
+static void snmp_seq_show_tcp_rtomin(struct seq_file *seq, struct net *net,
+				     unsigned long val)
+{
+	int sysctl_rtomin = READ_ONCE(net->ipv4.sysctl_tcp_rto_min_us);
+
+	if (tcp_rtax_rtomin)
+		seq_printf(seq, " %u", tcp_rtax_rtomin);
+	else if (sysctl_rtomin != jiffies_to_usecs(TCP_RTO_MIN))
+		seq_printf(seq, " %lu", usecs_to_jiffies(sysctl_rtomin));
+	else
+		seq_printf(seq, " %lu", val);
+}
+
 static int snmp_seq_show_tcp_udp(struct seq_file *seq, void *v)
 {
 	unsigned long buff[TCPUDP_MIB_MAX];
@@ -429,8 +442,7 @@ static int snmp_seq_show_tcp_udp(struct seq_file *seq, void *v)
 		if (snmp4_tcp_list[i].entry == TCP_MIB_MAXCONN)
 			seq_printf(seq, " %ld", buff[i]);
 		else if (snmp4_tcp_list[i].entry == TCP_MIB_RTOMIN)
-			seq_printf(seq, " %lu",
-				   tcp_rtax_rtomin ? tcp_rtax_rtomin : buff[i]);
+			snmp_seq_show_tcp_rtomin(seq, net, buff[i]);
 		else
 			seq_printf(seq, " %lu", buff[i]);
 	}
-- 
2.37.3