tcp: fix TCP_DEFER_ACCEPT retrans calculation

Fix TCP_DEFER_ACCEPT conversion between seconds and
retransmission to match the TCP SYN-ACK retransmission periods
because the time is converted to such retransmissions. The old
algorithm selects one more retransmission in some cases. Allow
up to 255 retransmissions.

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 64d0af6..9b2756f 100644 (file)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -326,6 +326,43 @@ void tcp_enter_memory_pressure(struct sock *sk)
 
 EXPORT_SYMBOL(tcp_enter_memory_pressure);
 
+/* Convert seconds to retransmits based on initial and max timeout */
+static u8 secs_to_retrans(int seconds, int timeout, int rto_max)
+{
+       u8 res = 0;
+
+       if (seconds > 0) {
+               int period = timeout;
+
+               res = 1;
+               while (seconds > period && res < 255) {
+                       res++;
+                       timeout <<= 1;
+                       if (timeout > rto_max)
+                               timeout = rto_max;
+                       period += timeout;
+               }
+       }
+       return res;
+}
+
+/* Convert retransmits to seconds based on initial and max timeout */
+static int retrans_to_secs(u8 retrans, int timeout, int rto_max)
+{
+       int period = 0;
+
+       if (retrans > 0) {
+               period = timeout;
+               while (--retrans) {
+                       timeout <<= 1;
+                       if (timeout > rto_max)
+                               timeout = rto_max;
+                       period += timeout;
+               }
+       }
+       return period;
+}
+
 /*
  *     Wait for a TCP event.
  *
@@ -2163,16 +2200,10 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
                break;
 
        case TCP_DEFER_ACCEPT:
-               icsk->icsk_accept_queue.rskq_defer_accept = 0;
-               if (val > 0) {
-                       /* Translate value in seconds to number of
-                        * retransmits */
-                       while (icsk->icsk_accept_queue.rskq_defer_accept < 32 &&
-                              val > ((TCP_TIMEOUT_INIT / HZ) <<
-                                      icsk->icsk_accept_queue.rskq_defer_accept))
-                               icsk->icsk_accept_queue.rskq_defer_accept++;
-                       icsk->icsk_accept_queue.rskq_defer_accept++;
-               }
+               /* Translate value in seconds to number of retransmits */
+               icsk->icsk_accept_queue.rskq_defer_accept =
+                       secs_to_retrans(val, TCP_TIMEOUT_INIT / HZ,
+                                       TCP_RTO_MAX / HZ);
                break;
 
        case TCP_WINDOW_CLAMP:
@@ -2353,8 +2384,8 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
                        val = (val ? : sysctl_tcp_fin_timeout) / HZ;
                break;
        case TCP_DEFER_ACCEPT:
-               val = !icsk->icsk_accept_queue.rskq_defer_accept ? 0 :
-                       ((TCP_TIMEOUT_INIT / HZ) << (icsk->icsk_accept_queue.rskq_defer_accept - 1));
+               val = retrans_to_secs(icsk->icsk_accept_queue.rskq_defer_accept,
+                                     TCP_TIMEOUT_INIT / HZ, TCP_RTO_MAX / HZ);
                break;
        case TCP_WINDOW_CLAMP:
                val = tp->window_clamp;