[PATCH 5.4 013/154] netpoll: hold rcu read lock in __netpoll_send_skb()

Greg Kroah-Hartman
2025-04-08T12:02:46Z

From: Breno Leitao <leitao@debian.org>

[ Upstream commit 505ead7ab77f289f12d8a68ac83da068e4d4408b ]

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@debian.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250306-netpoll_rcu_v2-v2-1-bc4f5c51742a@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/core/netpoll.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index 408fc07007900..940d371f5f3b5 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -326,6 +326,7 @@ static int netpoll_owner_active(struct net_device *dev)
static netdev_tx_t __netpoll_send_skb(struct netpoll *np, struct sk_buff *skb)
{
netdev_tx_t status = NETDEV_TX_BUSY;
+ netdev_tx_t ret = NET_XMIT_DROP;
struct net_device *dev;
unsigned long tries;
/* It is up to the caller to keep npinfo alive. */
@@ -334,11 +335,12 @@ static netdev_tx_t __netpoll_send_skb(struct netpoll *np, struct sk_buff *skb)
lockdep_assert_irqs_disabled();

dev = np->dev;
+ rcu_read_lock();
npinfo = rcu_dereference_bh(dev->npinfo);

if (!npinfo || !netif_running(dev) || !netif_device_present(dev)) {
dev_kfree_skb_irq(skb);
- return NET_XMIT_DROP;
+ goto out;
}

/* don't get messages out of order, and no recursion */
@@ -377,7 +379,10 @@ static netdev_tx_t __netpoll_send_skb(struct netpoll *np, struct sk_buff *skb)
skb_queue_tail(&npinfo->txq, skb);
schedule_delayed_work(&npinfo->tx_work,0);
}
- return NETDEV_TX_OK;
+ ret = NETDEV_TX_OK;
+out:
+ rcu_read_unlock();
+ return ret;
}

netdev_tx_t netpoll_send_skb(struct netpoll *np, struct sk_buff *skb)
--
2.39.5