[PATCH net] net/sched: sch_fq_pie: annotate data-races in fq_pie_dump_stats()

[PATCH net] net/sched: sch_fq_pie: annotate data-races in fq_pie_dump_stats()

[Eric Dumazet]

fq_codel_dump_stats() acquires the qdisc spinlock a bit too late.

Move this acquisition before we fill tc_fq_pie_xstats with live data.

Alternative would be to add READ_ONCE() and WRITE_ONCE() annotations,
but the spinlock is needed anyway to scan q->new_flows and q->old_flows.

Fixes: ec97ecf1ebe4 ("net: sched: add Flow Queue PIE packet scheduler")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Jamal Hadi Salim <jhs@mojatatu.com>
---
 net/sched/sch_fq_pie.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/net/sched/sch_fq_pie.c b/net/sched/sch_fq_pie.c
index 154c70f489f289066db5d61bb51e58aaf328f16e..7becbf5362b3165bac4517f32887386b01301612 100644
--- a/net/sched/sch_fq_pie.c
+++ b/net/sched/sch_fq_pie.c
@@ -509,18 +509,19 @@ static int fq_pie_dump(struct Qdisc *sch, struct sk_buff *skb)
 static int fq_pie_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
 {
 	struct fq_pie_sched_data *q = qdisc_priv(sch);
-	struct tc_fq_pie_xstats st = {
-		.packets_in	= q->stats.packets_in,
-		.overlimit	= q->stats.overlimit,
-		.overmemory	= q->overmemory,
-		.dropped	= q->stats.dropped,
-		.ecn_mark	= q->stats.ecn_mark,
-		.new_flow_count = q->new_flow_count,
-		.memory_usage   = q->memory_usage,
-	};
+	struct tc_fq_pie_xstats st = { 0 };
 	struct list_head *pos;
 
 	sch_tree_lock(sch);
+
+	st.packets_in	= q->stats.packets_in;
+	st.overlimit	= q->stats.overlimit;
+	st.overmemory	= q->overmemory;
+	st.dropped	= q->stats.dropped;
+	st.ecn_mark	= q->stats.ecn_mark;
+	st.new_flow_count = q->new_flow_count;
+	st.memory_usage   = q->memory_usage;
+
 	list_for_each(pos, &q->new_flows)
 		st.new_flows_len++;
 
-- 
2.54.0.rc2.544.gc7ae2d5bb8-goog

Re: [PATCH net] net/sched: sch_fq_pie: annotate data-races in fq_pie_dump_stats()

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu, 23 Apr 2026 06:35:27 +0000 you wrote:
> fq_codel_dump_stats() acquires the qdisc spinlock a bit too late.
> 
> Move this acquisition before we fill tc_fq_pie_xstats with live data.
> 
> Alternative would be to add READ_ONCE() and WRITE_ONCE() annotations,
> but the spinlock is needed anyway to scan q->new_flows and q->old_flows.
> 
> [...]

Here is the summary with links:
  - [net] net/sched: sch_fq_pie: annotate data-races in fq_pie_dump_stats()
    https://git.kernel.org/netdev/net/c/59b145771c79

You are awesome, thank you!
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