[PATCH net 3/5] net/sched: sch_cake: annotate data-races in cake_dump_stats() (III)

[Eric Dumazet <edumazet@google.com>]

cake_dump_stats() runs without qdisc spinlock being held.

In this third patch, I add READ_ONCE()/WRITE_ONCE() annotations
for the following fields:

- packets
- tin_dropped
- tin_ecn_mark
- ack_drops
- peak_delay
- avge_delay
- base_delay

Other annotations are added in following patches, to ease code review.

Fixes: 046f6fd5daef ("sched: Add Common Applications Kept Enhanced (cake) qdisc")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: "Toke Høiland-Jørgensen" <toke@toke.dk>
---
 net/sched/sch_cake.c | 38 ++++++++++++++++++++------------------
 1 file changed, 20 insertions(+), 18 deletions(-)

diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
index d7465ee4c5507467effd5aaaf8cfd05bcafde2cf..c5aae31565e984e40937b55201b498174a37180e 100644
--- a/net/sched/sch_cake.c
+++ b/net/sched/sch_cake.c
@@ -1600,7 +1600,7 @@ static unsigned int cake_drop(struct Qdisc *sch, struct sk_buff **to_free)
 	sch->qstats.backlog -= len;
 
 	flow->dropped++;
-	b->tin_dropped++;
+	WRITE_ONCE(b->tin_dropped, b->tin_dropped + 1);
 
 	if (q->config->rate_flags & CAKE_FLAG_INGRESS)
 		cake_advance_shaper(q, b, skb, now, true);
@@ -1820,7 +1820,7 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 			numsegs++;
 			slen += segs->len;
 			q->buffer_used += segs->truesize;
-			b->packets++;
+			WRITE_ONCE(b->packets, b->packets + 1);
 		}
 
 		/* stats */
@@ -1844,7 +1844,7 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 			ack = cake_ack_filter(q, flow);
 
 		if (ack) {
-			b->ack_drops++;
+			WRITE_ONCE(b->ack_drops, b->ack_drops + 1);
 			sch->qstats.drops++;
 			ack_pkt_len = qdisc_pkt_len(ack);
 			b->bytes += ack_pkt_len;
@@ -1860,7 +1860,7 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		}
 
 		/* stats */
-		b->packets++;
+		WRITE_ONCE(b->packets, b->packets + 1);
 		b->bytes	    += len - ack_pkt_len;
 		b->backlogs[idx]    += len - ack_pkt_len;
 		b->tin_backlog      += len - ack_pkt_len;
@@ -2236,7 +2236,7 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch)
 			b->tin_deficit -= len;
 		}
 		flow->dropped++;
-		b->tin_dropped++;
+		WRITE_ONCE(b->tin_dropped, b->tin_dropped + 1);
 		qdisc_tree_reduce_backlog(sch, 1, qdisc_pkt_len(skb));
 		qdisc_qstats_drop(sch);
 		qdisc_dequeue_drop(sch, skb, reason);
@@ -2244,17 +2244,19 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch)
 			goto retry;
 	}
 
-	b->tin_ecn_mark += !!flow->cvars.ecn_marked;
+	WRITE_ONCE(b->tin_ecn_mark, b->tin_ecn_mark + !!flow->cvars.ecn_marked);
 	qdisc_bstats_update(sch, skb);
 	WRITE_ONCE(q->last_active, now);
 
 	/* collect delay stats */
 	delay = ktime_to_ns(ktime_sub(now, cobalt_get_enqueue_time(skb)));
-	b->avge_delay = cake_ewma(b->avge_delay, delay, 8);
-	b->peak_delay = cake_ewma(b->peak_delay, delay,
-				  delay > b->peak_delay ? 2 : 8);
-	b->base_delay = cake_ewma(b->base_delay, delay,
-				  delay < b->base_delay ? 2 : 8);
+	WRITE_ONCE(b->avge_delay, cake_ewma(b->avge_delay, delay, 8));
+	WRITE_ONCE(b->peak_delay,
+		   cake_ewma(b->peak_delay, delay,
+			     delay > b->peak_delay ? 2 : 8));
+	WRITE_ONCE(b->base_delay,
+		   cake_ewma(b->base_delay, delay,
+			     delay < b->base_delay ? 2 : 8));
 
 	len = cake_advance_shaper(q, b, skb, now, false);
 	flow->deficit -= len;
@@ -3042,17 +3044,17 @@ static int cake_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
 		PUT_TSTAT_U32(INTERVAL_US,
 			      ktime_to_us(ns_to_ktime(b->cparams.interval)));
 
-		PUT_TSTAT_U32(SENT_PACKETS, b->packets);
-		PUT_TSTAT_U32(DROPPED_PACKETS, b->tin_dropped);
-		PUT_TSTAT_U32(ECN_MARKED_PACKETS, b->tin_ecn_mark);
-		PUT_TSTAT_U32(ACKS_DROPPED_PACKETS, b->ack_drops);
+		PUT_TSTAT_U32(SENT_PACKETS, READ_ONCE(b->packets));
+		PUT_TSTAT_U32(DROPPED_PACKETS, READ_ONCE(b->tin_dropped));
+		PUT_TSTAT_U32(ECN_MARKED_PACKETS, READ_ONCE(b->tin_ecn_mark));
+		PUT_TSTAT_U32(ACKS_DROPPED_PACKETS, READ_ONCE(b->ack_drops));
 
 		PUT_TSTAT_U32(PEAK_DELAY_US,
-			      ktime_to_us(ns_to_ktime(b->peak_delay)));
+			      ktime_to_us(ns_to_ktime(READ_ONCE(b->peak_delay))));
 		PUT_TSTAT_U32(AVG_DELAY_US,
-			      ktime_to_us(ns_to_ktime(b->avge_delay)));
+			      ktime_to_us(ns_to_ktime(READ_ONCE(b->avge_delay))));
 		PUT_TSTAT_U32(BASE_DELAY_US,
-			      ktime_to_us(ns_to_ktime(b->base_delay)));
+			      ktime_to_us(ns_to_ktime(READ_ONCE(b->base_delay))));
 
 		PUT_TSTAT_U32(WAY_INDIRECT_HITS, READ_ONCE(b->way_hits));
 		PUT_TSTAT_U32(WAY_MISSES, READ_ONCE(b->way_misses));
-- 
2.54.0.rc2.544.gc7ae2d5bb8-goog