netdev - [PATCH net-next] dql: annotate data-races around dql->last_obj

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Message-ID: <20241029191425.2519085-1-edumazet@google.com>
Date: Tue, 29 Oct 2024 19:14:25 +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: netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next] dql: annotate data-races around dql->last_obj_cnt

dql->last_obj_cnt is read/written from different contexts,
without any lock synchronization.

Use READ_ONCE()/WRITE_ONCE() to avoid load/store tearing.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/linux/dynamic_queue_limits.h | 2 +-
 lib/dynamic_queue_limits.c           | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/dynamic_queue_limits.h b/include/linux/dynamic_queue_limits.h
index 281298e77a1579cba1f92a3b3f03b8be089fd38f..808b1a5102e7c0bbbcd9676b0dacadad2f0ee49a 100644
--- a/include/linux/dynamic_queue_limits.h
+++ b/include/linux/dynamic_queue_limits.h
@@ -127,7 +127,7 @@ static inline void dql_queued(struct dql *dql, unsigned int count)
 	if (WARN_ON_ONCE(count > DQL_MAX_OBJECT))
 		return;
 
-	dql->last_obj_cnt = count;
+	WRITE_ONCE(dql->last_obj_cnt, count);
 
 	/* We want to force a write first, so that cpu do not attempt
 	 * to get cache line containing last_obj_cnt, num_queued, adj_limit
diff --git a/lib/dynamic_queue_limits.c b/lib/dynamic_queue_limits.c
index e49deddd3de9fe9e98d6712559cf48d12a0a2537..c1b7638a594ac43f947e00decabbd3468dcb53de 100644
--- a/lib/dynamic_queue_limits.c
+++ b/lib/dynamic_queue_limits.c
@@ -179,7 +179,7 @@ void dql_completed(struct dql *dql, unsigned int count)
 
 	dql->adj_limit = limit + completed;
 	dql->prev_ovlimit = ovlimit;
-	dql->prev_last_obj_cnt = dql->last_obj_cnt;
+	dql->prev_last_obj_cnt = READ_ONCE(dql->last_obj_cnt);
 	dql->num_completed = completed;
 	dql->prev_num_queued = num_queued;
 
-- 
2.47.0.163.g1226f6d8fa-goog