Commit 21742be8 authored by Jakub Kicinski's avatar Jakub Kicinski
Browse files

Merge branch 'netpoll-use-rcu-primitives-for-npinfo-pointer-access' 

Breno Leitao says:

====================
netpoll: Use RCU primitives for npinfo pointer access

The net_device->npinfo pointer is marked with __rcu, indicating it requires
proper RCU access primitives:

  struct net_device {
	...
	struct netpoll_info __rcu *npinfo;
	...
  };

Direct access to this pointer can lead to issues such as:
- Compiler incorrectly caching/reusing stale pointer values
- Missing memory ordering guarantees
- Non-atomic pointer loads

Replace direct NULL checks of npinfo with rcu_access_pointer(),
which provides the necessary memory ordering guarantees without the
overhead of a full RCU dereference, since we only need to verify
if the pointer is NULL.

In both cases, the RCU read lock is not held when the function is being
called. I checked that by using lockdep_assert_in_rcu_read_lock(), and
seeing the warning on both cases.
====================

Link: https://patch.msgid.link/20241118-netpoll_rcu-v1-0-a1888dcb4a02@debian.org


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parents 4262bacb a57d5a72

include/linux/netpoll.h

+1 −1
Original line number Diff line number Diff line
@@ -72,7 +72,7 @@ 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)

net/core/netpoll.c

+1 −1
Original line number Diff line number Diff line
@@ -626,7 +626,7 @@ 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;