linux-kernel - [PATCH AUTOSEL 4.19 21/21] netpoll: Use rcu_access_pointer() in __netpoll

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Message-ID: <20241124135709.3351371-21-sashal@kernel.org>
Date: Sun, 24 Nov 2024 08:56:54 -0500
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Breno Leitao <leitao@...ian.org>,
	Michal Kubiak <michal.kubiak@...el.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Sasha Levin <sashal@...nel.org>,
	davem@...emloft.net,
	edumazet@...gle.com,
	pabeni@...hat.com,
	horms@...nel.org,
	viro@...iv.linux.org.uk,
	netdev@...r.kernel.org
Subject: [PATCH AUTOSEL 4.19 21/21] netpoll: Use rcu_access_pointer() in __netpoll_setup

From: Breno Leitao <leitao@...ian.org>

[ Upstream commit c69c5e10adb903ae2438d4f9c16eccf43d1fcbc1 ]

The ndev->npinfo pointer in __netpoll_setup() is RCU-protected but is being
accessed directly for a NULL check. While no RCU read lock is held in this
context, we should still use proper RCU primitives for consistency and
correctness.

Replace the direct NULL check with rcu_access_pointer(), which is the
appropriate primitive when only checking for NULL without dereferencing
the pointer. This function provides the necessary ordering guarantees
without requiring RCU read-side protection.

Reviewed-by: Michal Kubiak <michal.kubiak@...el.com>
Signed-off-by: Breno Leitao <leitao@...ian.org>
Link: https://patch.msgid.link/20241118-netpoll_rcu-v1-1-a1888dcb4a02@debian.org
Signed-off-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 net/core/netpoll.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 08f0da9e6a809..0df6ae0fb71e5 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -616,7 +616,7 @@ int __netpoll_setup(struct netpoll *np, struct net_device *ndev)
 		goto out;
 	}
 
-	if (!ndev->npinfo) {
+	if (!rcu_access_pointer(ndev->npinfo)) {
 		npinfo = kmalloc(sizeof(*npinfo), GFP_KERNEL);
 		if (!npinfo) {
 			err = -ENOMEM;
-- 
2.43.0