pkt_sched: fq: use proper locking in fq_dump_stats()

commit 695b4ec0 upstream.

When fq is used on 32bit kernels, we need to lock the qdisc before
copying 64bit fields.

Otherwise "tc -s qdisc ..." might report bogus values.

Fixes: afe4fd06 ("pkt_sched: fq: Fair Queue packet scheduler")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16: keep using ktime_to_ns(ktime_get())]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

net/sched/sch_fq.c

@@ -789,20 +789,24 @@ static int fq_dump(struct Qdisc *sch, struct sk_buff *skb)
 static int fq_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
 {
 	struct fq_sched_data *q = qdisc_priv(sch);
-	u64 now = ktime_to_ns(ktime_get());
-	struct tc_fq_qd_stats st = {
-		.gc_flows		= q->stat_gc_flows,
-		.highprio_packets	= q->stat_internal_packets,
-		.tcp_retrans		= q->stat_tcp_retrans,
-		.throttled		= q->stat_throttled,
-		.flows_plimit		= q->stat_flows_plimit,
-		.pkts_too_long		= q->stat_pkts_too_long,
-		.allocation_errors	= q->stat_allocation_errors,
-		.flows			= q->flows,
-		.inactive_flows		= q->inactive_flows,
-		.throttled_flows	= q->throttled_flows,
-		.time_next_delayed_flow	= q->time_next_delayed_flow - now,
-	};
+	struct tc_fq_qd_stats st;
+
+	sch_tree_lock(sch);
+
+	st.gc_flows		  = q->stat_gc_flows;
+	st.highprio_packets	  = q->stat_internal_packets;
+	st.tcp_retrans		  = q->stat_tcp_retrans;
+	st.throttled		  = q->stat_throttled;
+	st.flows_plimit		  = q->stat_flows_plimit;
+	st.pkts_too_long	  = q->stat_pkts_too_long;
+	st.allocation_errors	  = q->stat_allocation_errors;
+	st.time_next_delayed_flow = q->time_next_delayed_flow - ktime_to_ns(ktime_get());
+	st.flows		  = q->flows;
+	st.inactive_flows	  = q->inactive_flows;
+	st.throttled_flows	  = q->throttled_flows;
+	st.pad			  = 0;
+
+	sch_tree_unlock(sch);
 
 	return gnet_stats_copy_app(d, &st, sizeof(st));
 }