netdev - [PATCH v2 net-next 01/11] net_sched: act: annotate data-races in tcf_lastuse_update() and tcf_tm

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Message-ID: <20250709090204.797558-2-edumazet@google.com>
Date: Wed,  9 Jul 2025 09:01:53 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>, Jamal Hadi Salim <jhs@...atatu.com>, 
	Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>, 
	Kuniyuki Iwashima <kuniyu@...gle.com>, netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH v2 net-next 01/11] net_sched: act: annotate data-races in
 tcf_lastuse_update() and tcf_tm_dump()

tcf_tm_dump() reads fields that can be changed concurrently,
and tcf_lastuse_update() might race against itself.

Add READ_ONCE() and WRITE_ONCE() annotations.

Fetch jiffies once in tcf_tm_dump().

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/net/act_api.h | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/include/net/act_api.h b/include/net/act_api.h
index 04781c92b43d6ab9cc6c81a88d5c6fe8c282c590..2894cfff2da3fba2b6e197dea35134e2aad5af80 100644
--- a/include/net/act_api.h
+++ b/include/net/act_api.h
@@ -76,19 +76,24 @@ static inline void tcf_lastuse_update(struct tcf_t *tm)
 {
 	unsigned long now = jiffies;
 
-	if (tm->lastuse != now)
-		tm->lastuse = now;
-	if (unlikely(!tm->firstuse))
-		tm->firstuse = now;
+	if (READ_ONCE(tm->lastuse) != now)
+		WRITE_ONCE(tm->lastuse, now);
+	if (unlikely(!READ_ONCE(tm->firstuse)))
+		WRITE_ONCE(tm->firstuse, now);
 }
 
 static inline void tcf_tm_dump(struct tcf_t *dtm, const struct tcf_t *stm)
 {
-	dtm->install = jiffies_to_clock_t(jiffies - stm->install);
-	dtm->lastuse = jiffies_to_clock_t(jiffies - stm->lastuse);
-	dtm->firstuse = stm->firstuse ?
-		jiffies_to_clock_t(jiffies - stm->firstuse) : 0;
-	dtm->expires = jiffies_to_clock_t(stm->expires);
+	unsigned long firstuse, now = jiffies;
+
+	dtm->install = jiffies_to_clock_t(now - READ_ONCE(stm->install));
+	dtm->lastuse = jiffies_to_clock_t(now - READ_ONCE(stm->lastuse));
+
+	firstuse = READ_ONCE(stm->firstuse);
+	dtm->firstuse = firstuse ?
+		jiffies_to_clock_t(now - firstuse) : 0;
+
+	dtm->expires = jiffies_to_clock_t(READ_ONCE(stm->expires));
 }
 
 static inline enum flow_action_hw_stats tc_act_hw_stats(u8 hw_stats)
-- 
2.50.0.727.gbf7dc18ff4-goog