[PATCH 6.1 751/969] net/sched: sch_fq_pie: annotate data-races in fq_pie_dump_stats()

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

6.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 59b145771c7982cfe9020d4e9e22da92d6b5ae31 ]

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>
Link: https://patch.msgid.link/20260423063527.2568262-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 607c580d75e4b..4bd5ca9acc53f 100644
--- a/net/sched/sch_fq_pie.c
+++ b/net/sched/sch_fq_pie.c
@@ -498,18 +498,19 @@ 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++;
 
-- 
2.53.0