[PATCH net-next 11/15] net_sched: sch_hhf: annotate data-races in hhf_dump_stats()

Eric Dumazet
2026-04-08T12:56:34Z

hhf_dump_stats() only runs with RTNL held,
reading 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>
---
net/sched/sch_hhf.c | 19 ++++++++++---------
1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/net/sched/sch_hhf.c b/net/sched/sch_hhf.c
index 69b6f0a5471cb9a3b7b760144683f2b249091d89..1e25b75daae2e5de31bd212dfa1f6d7aea927174 100644
--- a/net/sched/sch_hhf.c
+++ b/net/sched/sch_hhf.c
@@ -198,7 +198,8 @@ static struct hh_flow_state *seek_list(const u32 hash,
return NULL;
list_del(&flow->flowchain);
kfree(flow);
- q->hh_flows_current_cnt--;
+ WRITE_ONCE(q->hh_flows_current_cnt,
+ q->hh_flows_current_cnt - 1);
} else if (flow->hash_id == hash) {
return flow;
}
@@ -226,7 +227,7 @@ static struct hh_flow_state *alloc_new_hh(struct list_head *head,
}

if (q->hh_flows_current_cnt >= q->hh_flows_limit) {
- q->hh_flows_overlimit++;
+ WRITE_ONCE(q->hh_flows_overlimit, q->hh_flows_overlimit + 1);
return NULL;
}
/* Create new entry. */
@@ -234,7 +235,7 @@ static struct hh_flow_state *alloc_new_hh(struct list_head *head,
if (!flow)
return NULL;

- q->hh_flows_current_cnt++;
+ WRITE_ONCE(q->hh_flows_current_cnt, q->hh_flows_current_cnt + 1);
INIT_LIST_HEAD(&flow->flowchain);
list_add_tail(&flow->flowchain, head);

@@ -309,7 +310,7 @@ static enum wdrr_bucket_idx hhf_classify(struct sk_buff *skb, struct Qdisc *sch)
return WDRR_BUCKET_FOR_NON_HH;
flow->hash_id = hash;
flow->hit_timestamp = now;
- q->hh_flows_total_cnt++;
+ WRITE_ONCE(q->hh_flows_total_cnt, q->hh_flows_total_cnt + 1);

/* By returning without updating counters in q->hhf_arrays,
* we implicitly implement "shielding" (see Optimization O1).
@@ -404,7 +405,7 @@ static int hhf_enqueue(struct sk_buff *skb, struct Qdisc *sch,
return NET_XMIT_SUCCESS;

prev_backlog = sch->qstats.backlog;
- q->drop_overlimit++;
+ WRITE_ONCE(q->drop_overlimit, q->drop_overlimit + 1);
/* Return Congestion Notification only if we dropped a packet from this
* bucket.
*/
@@ -687,10 +688,10 @@ static int hhf_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
{
struct hhf_sched_data *q = qdisc_priv(sch);
struct tc_hhf_xstats st = {
- .drop_overlimit = q->drop_overlimit,
- .hh_overlimit = q->hh_flows_overlimit,
- .hh_tot_count = q->hh_flows_total_cnt,
- .hh_cur_count = q->hh_flows_current_cnt,
+ .drop_overlimit = READ_ONCE(q->drop_overlimit),
+ .hh_overlimit = READ_ONCE(q->hh_flows_overlimit),
+ .hh_tot_count = READ_ONCE(q->hh_flows_total_cnt),
+ .hh_cur_count = READ_ONCE(q->hh_flows_current_cnt),
};

return gnet_stats_copy_app(d, &st, sizeof(st));
--
2.53.0.1213.gd9a14994de-goog