[PATCH 5.4 085/321] netpoll: Use rcu_access_pointer() in netpoll_poll_lock

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5.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Breno Leitao <leitao@xxxxxxxxxx>

[ Upstream commit a57d5a72f8dec7db8a79d0016fb0a3bdecc82b56 ]

The ndev->npinfo pointer in netpoll_poll_lock() 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.

Fixes: bea3348eef27 ("[NET]: Make NAPI polling independent of struct net_device objects.")
Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
Reviewed-by: Michal Kubiak <michal.kubiak@xxxxxxxxx>
Link: https://patch.msgid.link/20241118-netpoll_rcu-v1-2-a1888dcb4a02@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 include/linux/netpoll.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/netpoll.h b/include/linux/netpoll.h
index 676f1ff161a98..3ff0303672842 100644
--- a/include/linux/netpoll.h
+++ b/include/linux/netpoll.h
@@ -78,7 +78,7 @@ static inline void *netpoll_poll_lock(struct napi_struct *napi)
 {
 	struct net_device *dev = napi->dev;
 
-	if (dev && dev->npinfo) {
+	if (dev && rcu_access_pointer(dev->npinfo)) {
 		int owner = smp_processor_id();
 
 		while (cmpxchg(&napi->poll_owner, -1, owner) != -1)
-- 
2.43.0







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