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Index: sys/netinet/tcp_input.c
===================================================================
--- sys/netinet/tcp_input.c
+++ sys/netinet/tcp_input.c
@@ -3408,7 +3408,7 @@
INP_WLOCK_ASSERT(tp->t_inpcb);
TCPSTAT_INC(tcps_rttupdated);
- tp->t_rttupdated++;
+ CEILINC(tp->t_rttupdated);
#ifdef STATS
stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_RTT,
imax(0, rtt * 1000 / hz));
Index: sys/netinet/tcp_stacks/bbr.c
===================================================================
--- sys/netinet/tcp_stacks/bbr.c
+++ sys/netinet/tcp_stacks/bbr.c
@@ -6515,7 +6515,7 @@
tp->t_rttbest = tp->t_srtt + tp->t_rttvar;
}
KMOD_TCPSTAT_INC(tcps_rttupdated);
- tp->t_rttupdated++;
+ CEILINC(tp->t_rttupdated);
#ifdef STATS
stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_RTT, imax(0, rtt_ticks));
#endif
Index: sys/netinet/tcp_stacks/rack.c
===================================================================
--- sys/netinet/tcp_stacks/rack.c
+++ sys/netinet/tcp_stacks/rack.c
@@ -3905,7 +3905,7 @@
}
KMOD_TCPSTAT_INC(tcps_rttupdated);
rack_log_rtt_upd(tp, rack, rtt, o_srtt, o_var);
- tp->t_rttupdated++;
+ CEILINC(tp->t_rttupdated);
#ifdef STATS
stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_RTT, imax(0, rtt));
#endif
Index: sys/netinet/tcp_usrreq.c
===================================================================
--- sys/netinet/tcp_usrreq.c
+++ sys/netinet/tcp_usrreq.c
@@ -2776,7 +2776,7 @@
tp->t_rttbest);
db_print_indent(indent);
- db_printf("t_rttupdated: %lu max_sndwnd: %u t_softerror: %d\n",
+ db_printf("t_rttupdated: %u max_sndwnd: %u t_softerror: %d\n",
tp->t_rttupdated, tp->max_sndwnd, tp->t_softerror);
db_print_indent(indent);
Index: sys/netinet/tcp_var.h
===================================================================
--- sys/netinet/tcp_var.h
+++ sys/netinet/tcp_var.h
@@ -182,7 +182,6 @@
uint32_t snd_ssthresh_prev; /* ssthresh prior to retransmit */
tcp_seq snd_recover_prev; /* snd_recover prior to retransmit */
int t_sndzerowin; /* zero-window updates sent */
- u_long t_rttupdated; /* number of times rtt sampled */
int snd_numholes; /* number of holes seen by sender */
u_int t_badrxtwin; /* window for retransmit recovery */
TAILQ_HEAD(sackhole_head, sackhole) snd_holes;
@@ -218,6 +217,7 @@
tcp_seq gput_seq; /* Outbound measurement seq */
tcp_seq gput_ack; /* Inbound measurement ack */
int32_t t_stats_gput_prev; /* XXXLAS: Prev gput measurement */
+ uint8_t t_rttupdated; /* number of times rtt sampled */
uint8_t t_tfo_client_cookie_len; /* TCP Fast Open client cookie length */
unsigned int *t_tfo_pending; /* TCP Fast Open server pending counter */
union {
@@ -511,6 +511,33 @@
max((tp)->t_rttmin, (((tp)->t_srtt >> (TCP_RTT_SHIFT - TCP_DELTA_SHIFT)) \
+ (tp)->t_rttvar) >> TCP_DELTA_SHIFT)
+/*
+ * Programmatically determine the maximum value of
+ * a signed or unsigned type, without integer overflow.
+ * Determining if the type of a variable is signed
+ * or not in a portable way without typeof() is quite
+ * involved but the resuting code is still optimal.
+ */
+#define UTYPE_MAX(x) \
+ ((((1 << (sizeof((x)) * 8 - 1)) - 1) * 2) + 1)
+#define TYPE_MAX(x) \
+ ((((1 << (sizeof((x)) * 8 - 2)) - 1) * 2) + 1)
+#define HIGH_BIT(n) \
+ ((n) & (1 << (sizeof(n) * 8 - 1)))
+#define IS_SIGNED(n) \
+ (HIGH_BIT(n) ? \
+ HIGH_BIT(n >> 1) != 0 : \
+ HIGH_BIT(~n >> 1) != 0)
+
+/*
+ * Macro to Post-increment counters that should NOT
+ * overflow, as a drop-in replacement for 'x++'.
+ */
+#define CEILINC(x) \
+ IS_SIGNED(x) ? \
+ ((x) < TYPE_MAX(x)) ? (x)++ : (x) : \
+ ((x) < UTYPE_MAX(x)) ? (x)++ : (x)
+
/*
* TCP statistics.
* Many of these should be kept per connection,

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