2 files changed, 11 insertions, 9 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 65cf90e063d5..227cba79fa6b 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -671,6 +671,7 @@ static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
 {
         struct tcp_sock *tp = tcp_sk(sk);
         long m = mrtt; /* RTT */
+        u32 srtt = tp->srtt;
 
         /*      The following amusing code comes from Jacobson's
          *      article in SIGCOMM '88.  Note that rtt and mdev
@@ -688,11 +689,9 @@ static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
          * does not matter how to _calculate_ it. Seems, it was trap
          * that VJ failed to avoid. 8)
          */
-        if (m == 0)
-                m = 1;
-        if (tp->srtt != 0) {
-                m -= (tp->srtt >> 3);   /* m is now error in rtt est */
-                tp->srtt += m;          /* rtt = 7/8 rtt + 1/8 new */
+        if (srtt != 0) {
+                m -= (srtt >> 3);       /* m is now error in rtt est */
+                srtt += m;              /* rtt = 7/8 rtt + 1/8 new */
                 if (m < 0) {
                         m = -m;         /* m is now abs(error) */
                         m -= (tp->mdev >> 2);   /* similar update on mdev */
@@ -723,11 +722,12 @@ static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
                 }
         } else {
                 /* no previous measure. */
-                tp->srtt = m << 3;      /* take the measured time to be rtt */
+                srtt = m << 3;          /* take the measured time to be rtt */
                 tp->mdev = m << 1;      /* make sure rto = 3*rtt */
                 tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
                 tp->rtt_seq = tp->snd_nxt;
         }
+        tp->srtt = max(1U, srtt);
 }
 
 /* Set the sk_pacing_rate to allow proper sizing of TSO packets.
@@ -746,8 +746,10 @@ static void tcp_update_pacing_rate(struct sock *sk)
 
         rate *= max(tp->snd_cwnd, tp->packets_out);
 
-        /* Correction for small srtt : minimum srtt being 8 (1 jiffy << 3),
-         * be conservative and assume srtt = 1 (125 us instead of 1.25 ms)
+        /* Correction for small srtt and scheduling constraints.
+         * For small rtt, consider noise is too high, and use
+         * the minimal value (srtt = 1 -> 125 us for HZ=1000)
+         *
          * We probably need usec resolution in the future.
          * Note: This also takes care of possible srtt=0 case,
          * when tcp_rtt_estimator() was not yet called.
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 03d26b85eab8..10435b3b9d0f 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1977,7 +1977,7 @@ bool tcp_schedule_loss_probe(struct sock *sk)
         /* Schedule a loss probe in 2*RTT for SACK capable connections
          * in Open state, that are either limited by cwnd or application.
          */
-        if (sysctl_tcp_early_retrans < 3 || !rtt || !tp->packets_out ||
+        if (sysctl_tcp_early_retrans < 3 || !tp->srtt || !tp->packets_out ||
             !tcp_is_sack(tp) || inet_csk(sk)->icsk_ca_state != TCP_CA_Open)
                 return false;