[PATCH net] net/sched: sch_choke: annotate data-races in choke_dump_stats()

[Eric Dumazet <edumazet@google.com>]

choke_dump_stats() only runs with RTNL held.
It reads fields that can be changed in qdisc fast path.
Add READ_ONCE()/WRITE_ONCE() annotations.

Fixes: edb09eb17ed8 ("net: sched: do not acquire qdisc spinlock in qdisc/class stats dump")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Jamal Hadi Salim <jhs@mojatatu.com>
---
 net/sched/sch_choke.c | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/net/sched/sch_choke.c b/net/sched/sch_choke.c
index 94df8e741a979191a06885ad3ee813f12650ff3c..2875bcdb18a413075c795665e95f9dbbaac45962 100644
--- a/net/sched/sch_choke.c
+++ b/net/sched/sch_choke.c
@@ -229,7 +229,7 @@ static int choke_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 
 		/* Draw a packet at random from queue and compare flow */
 		if (choke_match_random(q, skb, &idx)) {
-			q->stats.matched++;
+			WRITE_ONCE(q->stats.matched, q->stats.matched + 1);
 			choke_drop_by_idx(sch, idx, to_free);
 			goto congestion_drop;
 		}
@@ -241,11 +241,13 @@ static int choke_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 			qdisc_qstats_overlimit(sch);
 			if (use_harddrop(q) || !use_ecn(q) ||
 			    !INET_ECN_set_ce(skb)) {
-				q->stats.forced_drop++;
+				WRITE_ONCE(q->stats.forced_drop,
+					   q->stats.forced_drop + 1);
 				goto congestion_drop;
 			}
 
-			q->stats.forced_mark++;
+			WRITE_ONCE(q->stats.forced_mark,
+				   q->stats.forced_mark + 1);
 		} else if (++q->vars.qcount) {
 			if (red_mark_probability(p, &q->vars, q->vars.qavg)) {
 				q->vars.qcount = 0;
@@ -253,11 +255,13 @@ static int choke_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 
 				qdisc_qstats_overlimit(sch);
 				if (!use_ecn(q) || !INET_ECN_set_ce(skb)) {
-					q->stats.prob_drop++;
+					WRITE_ONCE(q->stats.prob_drop,
+					           q->stats.prob_drop + 1);
 					goto congestion_drop;
 				}
 
-				q->stats.prob_mark++;
+				WRITE_ONCE(q->stats.prob_mark,
+					   q->stats.prob_mark + 1);
 			}
 		} else
 			q->vars.qR = red_random(p);
@@ -272,7 +276,7 @@ static int choke_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		return NET_XMIT_SUCCESS;
 	}
 
-	q->stats.pdrop++;
+	WRITE_ONCE(q->stats.pdrop, q->stats.pdrop + 1);
 	return qdisc_drop(skb, sch, to_free);
 
 congestion_drop:
@@ -461,10 +465,12 @@ static int choke_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
 {
 	struct choke_sched_data *q = qdisc_priv(sch);
 	struct tc_choke_xstats st = {
-		.early	= q->stats.prob_drop + q->stats.forced_drop,
-		.marked	= q->stats.prob_mark + q->stats.forced_mark,
-		.pdrop	= q->stats.pdrop,
-		.matched = q->stats.matched,
+		.early	= READ_ONCE(q->stats.prob_drop) +
+			  READ_ONCE(q->stats.forced_drop),
+		.marked	= READ_ONCE(q->stats.prob_mark) +
+			  READ_ONCE(q->stats.forced_mark),
+		.pdrop	= READ_ONCE(q->stats.pdrop),
+		.matched = READ_ONCE(q->stats.matched),
 	};
 
 	return gnet_stats_copy_app(d, &st, sizeof(st));
-- 
2.54.0.rc2.544.gc7ae2d5bb8-goog