linux-kernel - [PATCH net] netpoll: guard __netpoll_send

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Message-Id: <20250303-netpoll_rcu_v2-v1-1-6b34d8a01fa2@debian.org>
Date: Mon, 03 Mar 2025 03:44:12 -0800
From: Breno Leitao <leitao@...ian.org>
To: "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
 Amerigo Wang <amwang@...hat.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
 kernel-team@...a.com, Breno Leitao <leitao@...ian.org>
Subject: [PATCH net] netpoll: guard __netpoll_send_skb() with RCU read lock

The function __netpoll_send_skb() is being invoked without holding the
RCU read lock. This oversight triggers a warning message when
CONFIG_PROVE_RCU_LIST is enabled:

	net/core/netpoll.c:330 suspicious rcu_dereference_check() usage!

	 netpoll_send_skb
	 netpoll_send_udp
	 write_ext_msg
	 console_flush_all
	 console_unlock
	 vprintk_emit

To prevent npinfo from disappearing unexpectedly, ensure that
__netpoll_send_skb() is protected with the RCU read lock.

Fixes: 2899656b494dcd1 ("netpoll: take rcu_read_lock_bh() in netpoll_send_skb_on_dev()")
Signed-off-by: Breno Leitao <leitao@...ian.org>
---
 net/core/netpoll.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 62b4041aae1ae..cac389105e2d1 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -326,6 +326,7 @@ static netdev_tx_t __netpoll_send_skb(struct netpoll *np, struct sk_buff *skb)

 	lockdep_assert_irqs_disabled();

+	guard(rcu)();
 	dev = np->dev;
 	npinfo = rcu_dereference_bh(dev->npinfo);

---
base-commit: 7eb172143d5508b4da468ed59ee857c6e5e01da6
change-id: 20250303-netpoll_rcu_v2-fed72eb0cb83

Best regards,
-- 
Breno Leitao <leitao@...ian.org>