netdev - [PATCH net] net: annotate data-races around cleanup_net

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Message-ID: <20250604093928.1323333-1-edumazet@google.com>
Date: Wed,  4 Jun 2025 09:39:28 +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>, netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net] net: annotate data-races around cleanup_net_task

from_cleanup_net() reads cleanup_net_task locklessly.

Add READ_ONCE()/WRITE_ONCE() annotations to avoid
a potential KCSAN warning, even if the race is harmless.

Fixes: 0734d7c3d93c ("net: expedite synchronize_net() for cleanup_net()")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/core/dev.c           | 2 +-
 net/core/net_namespace.c | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index a388f459a3666e3d186fb38d1eebd7cd33eb6979..be97c440ecd5f993344ae08d76c0b5216c4d296a 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -10499,7 +10499,7 @@ static void dev_index_release(struct net *net, int ifindex)
 static bool from_cleanup_net(void)
 {
 #ifdef CONFIG_NET_NS
-	return current == cleanup_net_task;
+	return current == READ_ONCE(cleanup_net_task);
 #else
 	return false;
 #endif
diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 42ee7fce3d95b5a2756d6a3780edba070f01ddb6..ae54f26709ca242567e5d62d7b5dcc7f6303da57 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -654,7 +654,7 @@ static void cleanup_net(struct work_struct *work)
 	struct net *net, *tmp, *last;
 	LIST_HEAD(net_exit_list);
 
-	cleanup_net_task = current;
+	WRITE_ONCE(cleanup_net_task, current);
 
 	/* Atomically snapshot the list of namespaces to cleanup */
 	net_kill_list = llist_del_all(&cleanup_list);
@@ -704,7 +704,7 @@ static void cleanup_net(struct work_struct *work)
 		put_user_ns(net->user_ns);
 		net_passive_dec(net);
 	}
-	cleanup_net_task = NULL;
+	WRITE_ONCE(cleanup_net_task, NULL);
 }
 
 /**
-- 
2.50.0.rc0.604.gd4ff7b7c86-goog