Re: [PATCH net 1/2] netpoll: Use rcu_access_pointer() in __netpoll_setup
From: Michal Kubiak
Date: Mon Nov 18 2024 - 07:18:55 EST
On Mon, Nov 18, 2024 at 03:15:17AM -0800, Breno Leitao wrote:
> 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.
>
> Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
> Fixes: 8fdd95ec162a ("netpoll: Allow netpoll_setup/cleanup recursion")
nitpick: Shouldn't the "Signed-off-by" tag go as the last one?
Thanks,
Reviewed-by: Michal Kubiak <michal.kubiak@xxxxxxxxx>
> ---
> 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 aa49b92e9194babab17b2e039daf092a524c5b88..45fb60bc4803958eb07d4038028269fc0c19622e 100644
> --- a/net/core/netpoll.c
> +++ b/net/core/netpoll.c
> @@ -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;
>
> --
> 2.43.5
>
>