netdev - [PATCH net-next 03/10] net: dst: annotate data-races around dst->lastuse

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Message-ID: <20250627112526.3615031-4-edumazet@google.com>
Date: Fri, 27 Jun 2025 11:25:19 +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>, Kuniyuki Iwashima <kuniyu@...gle.com>, 
	David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 03/10] net: dst: annotate data-races around dst->lastuse

(dst_entry)->lastuse is read and written locklessly,
add corresponding annotations.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/net/dst.h    | 4 ++--
 net/core/rtnetlink.c | 4 +++-
 net/ipv6/route.c     | 3 ++-
 3 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/include/net/dst.h b/include/net/dst.h
index 1efe1e5d51a904a0fe907687835b8e07f32afaec..bef2f41c7220437b3cb177ea8c85b81b3f89e8f8 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -240,9 +240,9 @@ static inline void dst_hold(struct dst_entry *dst)
 
 static inline void dst_use_noref(struct dst_entry *dst, unsigned long time)
 {
-	if (unlikely(time != dst->lastuse)) {
+	if (unlikely(time != READ_ONCE(dst->lastuse))) {
 		dst->__use++;
-		dst->lastuse = time;
+		WRITE_ONCE(dst->lastuse, time);
 	}
 }
 
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index c57692eb8da9d47c3b0943bf7b8d8b7f7d347836..a9555bfc372f5709a3b846343986dce1edf935be 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1026,9 +1026,11 @@ int rtnl_put_cacheinfo(struct sk_buff *skb, struct dst_entry *dst, u32 id,
 		.rta_error = error,
 		.rta_id =  id,
 	};
+	unsigned long delta;
 
 	if (dst) {
-		ci.rta_lastuse = jiffies_delta_to_clock_t(jiffies - dst->lastuse);
+		delta = jiffies - READ_ONCE(dst->lastuse);
+		ci.rta_lastuse = jiffies_delta_to_clock_t(delta);
 		ci.rta_used = dst->__use;
 		ci.rta_clntref = rcuref_read(&dst->__rcuref);
 	}
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 1014dcea1200cb4d4fc63f7b335fd2663c4844a3..375112a59492ea3654d180c504946d96ed1592cd 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2133,7 +2133,8 @@ static void rt6_age_examine_exception(struct rt6_exception_bucket *bucket,
 	 * expired, independently from their aging, as per RFC 8201 section 4
 	 */
 	if (!(rt->rt6i_flags & RTF_EXPIRES)) {
-		if (time_after_eq(now, rt->dst.lastuse + gc_args->timeout)) {
+		if (time_after_eq(now, READ_ONCE(rt->dst.lastuse) +
+				       gc_args->timeout)) {
 			pr_debug("aging clone %p\n", rt);
 			rt6_remove_exception(bucket, rt6_ex);
 			return;
-- 
2.50.0.727.gbf7dc18ff4-goog