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>

1 files changed, 43 insertions, 12 deletions

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 64d0af675823..9b2756fbdf9b 100644
--- 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;