Clamp the TCP retry timeout as Linux kernel does. If a retry occurs
during the handshake and the RTO is below 3 seconds, re-initialise
it to 3 seconds for data retransmissions according to RFC 6298.
Suggested-by: Stefano Brivio
Signed-off-by: Yumei Huang
---
tcp.c | 25 ++++++++++++++++++++-----
tcp.h | 2 ++
tcp_conn.h | 1 +
3 files changed, 23 insertions(+), 5 deletions(-)
diff --git a/tcp.c b/tcp.c
index cff23d1..3418705 100644
--- a/tcp.c
+++ b/tcp.c
@@ -187,6 +187,9 @@
* established connections, or (syn_retries + syn_linear_timeouts) times
* during the handshake, then reset the connection
*
+ * - RTO_INIT_AFTER_SYN_RETRIES: if SYN retries happened during handshake and
+ * RTO is less than this, re-initialise RTO to this for data retransmissions
+ *
* - FIN_TIMEOUT: if a FIN segment was sent to tap/guest (flag ACK_FROM_TAP_DUE
* with TAP_FIN_SENT event), and no ACK is received within this time, reset
* the connection
@@ -340,6 +343,7 @@ enum {
#define ACK_INTERVAL 10 /* ms */
#define RTO_INIT 1 /* s, RFC 6298 */
+#define RTO_INIT_AFTER_SYN_RETRIES 3 /* s, RFC 6298 */
#define FIN_TIMEOUT 60
#define ACT_TIMEOUT 7200
@@ -365,9 +369,11 @@ uint8_t tcp_migrate_rcv_queue [TCP_MIGRATE_RCV_QUEUE_MAX];
#define SYN_RETRIES "/proc/sys/net/ipv4/tcp_syn_retries"
#define SYN_LINEAR_TIMEOUTS "/proc/sys/net/ipv4/tcp_syn_linear_timeouts"
+#define RTO_MAX_MS "/proc/sys/net/ipv4/tcp_rto_max_ms"
#define SYN_RETRIES_DEFAULT 6
#define SYN_LINEAR_TIMEOUTS_DEFAULT 4
+#define RTO_MAX_DEFAULT 120 /* s */
#define MAX_SYNCNT 127 /* derived from kernel's limit */
/* "Extended" data (not stored in the flow table) for TCP flow migration */
@@ -392,7 +398,7 @@ static const char *tcp_state_str[] __attribute((__unused__)) = {
static const char *tcp_flag_str[] __attribute((__unused__)) = {
"STALLED", "LOCAL", "ACTIVE_CLOSE", "ACK_TO_TAP_DUE",
- "ACK_FROM_TAP_DUE", "ACK_FROM_TAP_BLOCKS",
+ "ACK_FROM_TAP_DUE", "ACK_FROM_TAP_BLOCKS", "SYN_RETRIED",
};
/* Listening sockets, used for automatic port forwarding in pasta mode only */
@@ -590,10 +596,13 @@ static void tcp_timer_ctl(const struct ctx *c, struct tcp_tap_conn *conn)
if (conn->flags & ACK_TO_TAP_DUE) {
it.it_value.tv_nsec = (long)ACK_INTERVAL * 1000 * 1000;
} else if (conn->flags & ACK_FROM_TAP_DUE) {
- int exp = conn->retries;
+ int exp = conn->retries, timeout = RTO_INIT;
if (!(conn->events & ESTABLISHED))
exp -= c->tcp.syn_linear_timeouts;
- it.it_value.tv_sec = RTO_INIT << MAX(exp, 0);
+ else if (conn->flags & SYN_RETRIED)
+ timeout = MAX(timeout, RTO_INIT_AFTER_SYN_RETRIES);
+ timeout <<= MAX(exp, 0);
+ it.it_value.tv_sec = MIN(timeout, c->tcp.rto_max);
} else if (CONN_HAS(conn, SOCK_FIN_SENT | TAP_FIN_ACKED)) {
it.it_value.tv_sec = FIN_TIMEOUT;
} else {
@@ -2441,6 +2450,7 @@ void tcp_timer_handler(const struct ctx *c, union epoll_ref ref)
flow_trace(conn, "SYN timeout, retry");
tcp_send_flag(c, conn, SYN);
conn->retries++;
+ conn_flag(c, conn, SYN_RETRIED);
tcp_timer_ctl(c, conn);
}
} else if (CONN_HAS(conn, SOCK_FIN_SENT | TAP_FIN_ACKED)) {
@@ -2812,10 +2822,15 @@ static void tcp_get_rto_params(struct ctx *c)
v = read_file_integer(SYN_LINEAR_TIMEOUTS, SYN_LINEAR_TIMEOUTS_DEFAULT);
c->tcp.syn_linear_timeouts = MIN(v, MAX_SYNCNT);
+ v = read_file_integer(RTO_MAX_MS, (intmax_t)(RTO_MAX_DEFAULT * 1000));
+ c->tcp.rto_max = MIN(DIV_ROUND_UP(v, 1000), INT_MAX);
+
debug("Using TCP RTO parameters, syn_retries: %"PRIu8
- ", syn_linear_timeouts: %"PRIu8,
+ ", syn_linear_timeouts: %"PRIu8
+ ", rto_max: %d",
c->tcp.syn_retries,
- c->tcp.syn_linear_timeouts);
+ c->tcp.syn_linear_timeouts,
+ c->tcp.rto_max);
}
/**
diff --git a/tcp.h b/tcp.h
index 37d7758..6fb6f92 100644
--- a/tcp.h
+++ b/tcp.h
@@ -60,6 +60,7 @@ union tcp_listen_epoll_ref {
* @fwd_out: Port forwarding configuration for outbound packets
* @timer_run: Timestamp of most recent timer run
* @pipe_size: Size of pipes for spliced connections
+ * @rto_max: Maximum retry timeout (in s)
* @syn_retries: SYN retries using exponential backoff timeout
* @syn_linear_timeouts: SYN retries before using exponential backoff timeout
*/
@@ -68,6 +69,7 @@ struct tcp_ctx {
struct fwd_ports fwd_out;
struct timespec timer_run;
size_t pipe_size;
+ int rto_max;
uint8_t syn_retries;
uint8_t syn_linear_timeouts;
};
diff --git a/tcp_conn.h b/tcp_conn.h
index 923af36..e36910c 100644
--- a/tcp_conn.h
+++ b/tcp_conn.h
@@ -77,6 +77,7 @@ struct tcp_tap_conn {
#define ACK_TO_TAP_DUE BIT(3)
#define ACK_FROM_TAP_DUE BIT(4)
#define ACK_FROM_TAP_BLOCKS BIT(5)
+#define SYN_RETRIED BIT(6)
#define SNDBUF_BITS 24
unsigned int sndbuf :SNDBUF_BITS;
--
2.51.1