net/sched/sch_htb: clamp xstats tokens to fit into 32-bit int

In kernel HTB keeps tokens in signed 64-bit in nanoseconds. In netlink
protocol these values are converted into pshed ticks (64ns for now) and
truncated to 32-bit. In struct tc_htb_xstats fields "tokens" and "ctokens"
are declared as unsigned 32-bit but they could be negative thus tool 'tc'
prints them as signed. Big values loose higher bits and/or become negative.

This patch clamps tokens in xstat into range from INT_MIN to INT_MAX.
In this way it's easier to understand what's going on here.
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_htb.c

@@ -1140,8 +1140,10 @@ htb_dump_class_stats(struct Qdisc *sch, unsigned long arg, struct gnet_dump *d)
 
 	if (!cl->level && cl->un.leaf.q)
 		qlen = cl->un.leaf.q->q.qlen;
-	cl->xstats.tokens = PSCHED_NS2TICKS(cl->tokens);
-	cl->xstats.ctokens = PSCHED_NS2TICKS(cl->ctokens);
+	cl->xstats.tokens = clamp_t(s64, PSCHED_NS2TICKS(cl->tokens),
+				    INT_MIN, INT_MAX);
+	cl->xstats.ctokens = clamp_t(s64, PSCHED_NS2TICKS(cl->ctokens),
+				     INT_MIN, INT_MAX);
 
 	if (gnet_stats_copy_basic(d, NULL, &cl->bstats) < 0 ||
 	    gnet_stats_copy_rate_est(d, NULL, &cl->rate_est) < 0 ||