[PATCH v2 net 4/5] net/sched: sch_cake: annotate data-races in cake_dump_stats() (IV)

Eric Dumazet
2026-04-27T08:36:15Z

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

- avg_peak_bandwidth
- buffer_limit
- buffer_max_used
- avg_netoff
- max_netlen
- max_adjlen
- min_netlen
- min_adjlen
- active_queues
- tin_rate_bps
- bytes
- tin_backlog

Other annotations are added in following patch, 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 | 90 ++++++++++++++++++++++----------------------
1 file changed, 46 insertions(+), 44 deletions(-)

diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
index c5aae31565e984e40937b55201b498174a37180e..975f5d6d6982f33a9d1f5454721ce16b6c433439 100644
--- a/net/sched/sch_cake.c
+++ b/net/sched/sch_cake.c
@@ -1379,9 +1379,9 @@ static u32 cake_calc_overhead(struct cake_sched_data *qd, u32 len, u32 off)
len -= off;

if (qd->max_netlen < len)
- qd->max_netlen = len;
+ WRITE_ONCE(qd->max_netlen, len);
if (qd->min_netlen > len)
- qd->min_netlen = len;
+ WRITE_ONCE(qd->min_netlen, len);

len += q->rate_overhead;

@@ -1401,9 +1401,9 @@ static u32 cake_calc_overhead(struct cake_sched_data *qd, u32 len, u32 off)
}

if (qd->max_adjlen < len)
- qd->max_adjlen = len;
+ WRITE_ONCE(qd->max_adjlen, len);
if (qd->min_adjlen > len)
- qd->min_adjlen = len;
+ WRITE_ONCE(qd->min_adjlen, len);

return len;
}
@@ -1416,7 +1416,7 @@ static u32 cake_overhead(struct cake_sched_data *q, const struct sk_buff *skb)
u16 segs = qdisc_pkt_segs(skb);
u32 len = qdisc_pkt_len(skb);

- q->avg_netoff = cake_ewma(q->avg_netoff, off << 16, 8);
+ WRITE_ONCE(q->avg_netoff, cake_ewma(q->avg_netoff, off << 16, 8));

if (segs == 1)
return cake_calc_overhead(q, len, off);
@@ -1596,7 +1596,7 @@ static unsigned int cake_drop(struct Qdisc *sch, struct sk_buff **to_free)
len = qdisc_pkt_len(skb);
q->buffer_used -= skb->truesize;
b->backlogs[idx] -= len;
- b->tin_backlog -= len;
+ WRITE_ONCE(b->tin_backlog, b->tin_backlog - len);
sch->qstats.backlog -= len;

flow->dropped++;
@@ -1824,11 +1824,11 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch,
}

/* stats */
- b->bytes += slen;
b->backlogs[idx] += slen;
- b->tin_backlog += slen;
sch->qstats.backlog += slen;
q->avg_window_bytes += slen;
+ WRITE_ONCE(b->bytes, b->bytes + slen);
+ WRITE_ONCE(b->tin_backlog, b->tin_backlog + slen);

qdisc_tree_reduce_backlog(sch, 1-numsegs, len-slen);
consume_skb(skb);
@@ -1847,7 +1847,7 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch,
WRITE_ONCE(b->ack_drops, b->ack_drops + 1);
sch->qstats.drops++;
ack_pkt_len = qdisc_pkt_len(ack);
- b->bytes += ack_pkt_len;
+ WRITE_ONCE(b->bytes, b->bytes + ack_pkt_len);
q->buffer_used += skb->truesize - ack->truesize;
if (q->config->rate_flags & CAKE_FLAG_INGRESS)
cake_advance_shaper(q, b, ack, now, true);
@@ -1861,11 +1861,11 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch,

/* stats */
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;
sch->qstats.backlog += len - ack_pkt_len;
q->avg_window_bytes += len - ack_pkt_len;
+ WRITE_ONCE(b->bytes, b->bytes + len - ack_pkt_len);
+ WRITE_ONCE(b->tin_backlog, b->tin_backlog + len - ack_pkt_len);
}

if (q->overflow_timeout)
@@ -1895,9 +1895,9 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch,
u64 b = q->avg_window_bytes * (u64)NSEC_PER_SEC;

b = div64_u64(b, window_interval);
- q->avg_peak_bandwidth =
- cake_ewma(q->avg_peak_bandwidth, b,
- b > q->avg_peak_bandwidth ? 2 : 8);
+ WRITE_ONCE(q->avg_peak_bandwidth,
+ cake_ewma(q->avg_peak_bandwidth, b,
+ b > q->avg_peak_bandwidth ? 2 : 8));
q->avg_window_bytes = 0;
q->avg_window_begin = now;

@@ -1938,7 +1938,7 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch,
}

if (q->buffer_used > q->buffer_max_used)
- q->buffer_max_used = q->buffer_used;
+ WRITE_ONCE(q->buffer_max_used, q->buffer_used);

if (q->buffer_used <= q->buffer_limit)
return NET_XMIT_SUCCESS;
@@ -1978,7 +1978,7 @@ static struct sk_buff *cake_dequeue_one(struct Qdisc *sch)
skb = dequeue_head(flow);
len = qdisc_pkt_len(skb);
b->backlogs[q->cur_flow] -= len;
- b->tin_backlog -= len;
+ WRITE_ONCE(b->tin_backlog, b->tin_backlog - len);
sch->qstats.backlog -= len;
q->buffer_used -= skb->truesize;
sch->q.qlen--;
@@ -2043,7 +2043,7 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch)

cake_configure_rates(sch, new_rate, true);
q->last_checked_active = now;
- q->active_queues = num_active_qs;
+ WRITE_ONCE(q->active_queues, num_active_qs);
}

begin:
@@ -2347,7 +2347,7 @@ static void cake_set_rate(struct cake_tin_data *b, u64 rate, u32 mtu,
/* else unlimited, ie. zero delay */
WRITE_ONCE(b->flow_quantum, 1514);
}
- b->tin_rate_bps = rate;
+ WRITE_ONCE(b->tin_rate_bps, rate);
b->tin_rate_ns = rate_ns;
b->tin_rate_shft = rate_shft;

@@ -2617,25 +2617,27 @@ static void cake_reconfigure(struct Qdisc *sch)
{
struct cake_sched_data *qd = qdisc_priv(sch);
struct cake_sched_config *q = qd->config;
+ u32 buffer_limit;

cake_configure_rates(sch, qd->config->rate_bps, false);

if (q->buffer_config_limit) {
- qd->buffer_limit = q->buffer_config_limit;
+ buffer_limit = q->buffer_config_limit;
} else if (q->rate_bps) {
u64 t = q->rate_bps * q->interval;

do_div(t, USEC_PER_SEC / 4);
- qd->buffer_limit = max_t(u32, t, 4U << 20);
+ buffer_limit = max_t(u32, t, 4U << 20);
} else {
- qd->buffer_limit = ~0;
+ buffer_limit = ~0;
}

sch->flags &= ~TCQ_F_CAN_BYPASS;

- qd->buffer_limit = min(qd->buffer_limit,
- max(sch->limit * psched_mtu(qdisc_dev(sch)),
- q->buffer_config_limit));
+ WRITE_ONCE(qd->buffer_limit,
+ min(buffer_limit,
+ max(sch->limit * psched_mtu(qdisc_dev(sch)),
+ q->buffer_config_limit)));
}

static int cake_config_change(struct cake_sched_config *q, struct nlattr *opt,
@@ -2780,10 +2782,10 @@ static int cake_change(struct Qdisc *sch, struct nlattr *opt,
return ret;

if (overhead_changed) {
- qd->max_netlen = 0;
- qd->max_adjlen = 0;
- qd->min_netlen = ~0;
- qd->min_adjlen = ~0;
+ WRITE_ONCE(qd->max_netlen, 0);
+ WRITE_ONCE(qd->max_adjlen, 0);
+ WRITE_ONCE(qd->min_netlen, ~0);
+ WRITE_ONCE(qd->min_adjlen, ~0);
}

if (qd->tins) {
@@ -3001,15 +3003,15 @@ static int cake_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
goto nla_put_failure; \
} while (0)

- PUT_STAT_U64(CAPACITY_ESTIMATE64, q->avg_peak_bandwidth);
- PUT_STAT_U32(MEMORY_LIMIT, q->buffer_limit);
- PUT_STAT_U32(MEMORY_USED, q->buffer_max_used);
- PUT_STAT_U32(AVG_NETOFF, ((q->avg_netoff + 0x8000) >> 16));
- PUT_STAT_U32(MAX_NETLEN, q->max_netlen);
- PUT_STAT_U32(MAX_ADJLEN, q->max_adjlen);
- PUT_STAT_U32(MIN_NETLEN, q->min_netlen);
- PUT_STAT_U32(MIN_ADJLEN, q->min_adjlen);
- PUT_STAT_U32(ACTIVE_QUEUES, q->active_queues);
+ PUT_STAT_U64(CAPACITY_ESTIMATE64, READ_ONCE(q->avg_peak_bandwidth));
+ PUT_STAT_U32(MEMORY_LIMIT, READ_ONCE(q->buffer_limit));
+ PUT_STAT_U32(MEMORY_USED, READ_ONCE(q->buffer_max_used));
+ PUT_STAT_U32(AVG_NETOFF, ((READ_ONCE(q->avg_netoff) + 0x8000) >> 16));
+ PUT_STAT_U32(MAX_NETLEN, READ_ONCE(q->max_netlen));
+ PUT_STAT_U32(MAX_ADJLEN, READ_ONCE(q->max_adjlen));
+ PUT_STAT_U32(MIN_NETLEN, READ_ONCE(q->min_netlen));
+ PUT_STAT_U32(MIN_ADJLEN, READ_ONCE(q->min_adjlen));
+ PUT_STAT_U32(ACTIVE_QUEUES, READ_ONCE(q->active_queues));

#undef PUT_STAT_U32
#undef PUT_STAT_U64
@@ -3035,9 +3037,9 @@ static int cake_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
if (!ts)
goto nla_put_failure;

- PUT_TSTAT_U64(THRESHOLD_RATE64, b->tin_rate_bps);
- PUT_TSTAT_U64(SENT_BYTES64, b->bytes);
- PUT_TSTAT_U32(BACKLOG_BYTES, b->tin_backlog);
+ PUT_TSTAT_U64(THRESHOLD_RATE64, READ_ONCE(b->tin_rate_bps));
+ PUT_TSTAT_U64(SENT_BYTES64, READ_ONCE(b->bytes));
+ PUT_TSTAT_U32(BACKLOG_BYTES, READ_ONCE(b->tin_backlog));

PUT_TSTAT_U32(TARGET_US,
ktime_to_us(ns_to_ktime(b->cparams.target)));
@@ -3304,10 +3306,10 @@ static int cake_mq_change(struct Qdisc *sch, struct nlattr *opt,
struct cake_sched_data *qd = qdisc_priv(chld);

if (overhead_changed) {
- qd->max_netlen = 0;
- qd->max_adjlen = 0;
- qd->min_netlen = ~0;
- qd->min_adjlen = ~0;
+ WRITE_ONCE(qd->max_netlen, 0);
+ WRITE_ONCE(qd->max_adjlen, 0);
+ WRITE_ONCE(qd->min_netlen, ~0);
+ WRITE_ONCE(qd->min_adjlen, ~0);
}

if (qd->tins) {
--
2.54.0.545.g6539524ca2-goog