Re: [PATCH] net: convert netdev_nl_sock bindings list to xarray

[Nikolay Aleksandrov]

On 10/08/2026 09:57, Shivaji Kant wrote:
> netdev_nl_sock previously used a struct list_head bindings to keep
> track of active netdev netlink bindings, protected by a per-socket
> struct mutex lock (priv->lock).
>
> Since list modifications and iterations are not concurrency-safe,
> priv->lock was introduced to serialize operations on priv->bindings.
> However, xarray manages its own internal locking (xa_lock) for store,
> erase, and iteration operations.
>
> Convert bindings in struct netdev_nl_sock from struct list_head to
> struct xarray and remove priv->lock. This simplifies the code by
> removing explicit mutex locking in netdev_nl_bind_rx_doit(),
> netdev_nl_bind_tx_doit(), and socket initialization/teardown functions.
>
> Reviewed-by: Mina Almasry <almasrymina@xxxxxxxxxx>
> Signed-off-by: Shivaji Kant <shivajikant@xxxxxxxxxx>
> ---
>   include/net/netdev_netlink.h |  5 ++---
>   net/core/devmem.c            | 13 ++++++++++---
>   net/core/devmem.h            |  4 ++--
>   net/core/netdev-genl.c       | 25 ++++++-------------------
>   4 files changed, 20 insertions(+), 27 deletions(-)

This patch should target net-next.

> diff --git a/include/net/netdev_netlink.h b/include/net/netdev_netlink.h
> index 075962dbe743..45a4a482d42e 100644
> --- a/include/net/netdev_netlink.h
> +++ b/include/net/netdev_netlink.h
> @@ -2,11 +2,10 @@
>   #ifndef __NET_NETDEV_NETLINK_H
>   #define __NET_NETDEV_NETLINK_H
>   
> -#include <linux/list.h>
> +#include <linux/xarray.h>
>   
>   struct netdev_nl_sock {
> -	struct mutex lock;
> -	struct list_head bindings;
> +	struct xarray bindings;
>   };
>   
>   #endif	/* __NET_NETDEV_NETLINK_H */
> diff --git a/net/core/devmem.c b/net/core/devmem.c
> index 957d6b96216b..52fda18b80ef 100644
> --- a/net/core/devmem.c
> +++ b/net/core/devmem.c
> @@ -134,8 +134,8 @@ void net_devmem_unbind_dmabuf(struct net_devmem_dmabuf_binding *binding)
>   	 */
>   	synchronize_net();
>   
> -	if (binding->list.next)
> -		list_del(&binding->list);
> +	if (binding->sock_priv)
> +		xa_erase(&binding->sock_priv->bindings, binding->id);
>   
>   	xa_for_each(&binding->bound_rxqs, xa_idx, rxq) {
>   		const struct pp_memory_provider_params mp_params = {
> @@ -193,6 +193,7 @@ net_devmem_bind_dmabuf(struct net_device *dev, void *vdev,
>   	struct dma_buf *dmabuf;
>   	unsigned int sg_idx, i;
>   	unsigned long virtual;
> +	void *res;
>   	int err;
>   
>   	if (!dma_dev) {
> @@ -325,7 +326,13 @@ net_devmem_bind_dmabuf(struct net_device *dev, void *vdev,
>   	if (err < 0)
>   		goto err_free_chunks;
>   
> -	list_add(&binding->list, &priv->bindings);
> +	binding->sock_priv = priv;
> +	res = xa_store(&priv->bindings, binding->id, binding, GFP_KERNEL);
> +	if (xa_is_err(res)) {
> +		err = xa_err(res);
> +		xa_erase(&net_devmem_dmabuf_bindings, binding->id);
> +		goto err_free_chunks;

This error cleans up after the previous xa_alloc_cyclic call itself instead
of following the style of the rest of the error cleanups. I'd move the xa_erase()
into its own err_ label and goto there.

> +	}
>   
>   	return binding;
>   
> diff --git a/net/core/devmem.h b/net/core/devmem.h
> index 3852a56036cb..bf77e5a9a8fe 100644
> --- a/net/core/devmem.h
> +++ b/net/core/devmem.h
> @@ -49,10 +49,10 @@ struct net_devmem_dmabuf_binding {
>   	 */
>   	struct percpu_ref ref;
>   
> -	/* The list of bindings currently active. Used for netlink to notify us
> +	/* The socket priv this binding belongs to. Used for netlink to notify us
>   	 * of the user dropping the bind.
>   	 */
> -	struct list_head list;
> +	struct netdev_nl_sock *sock_priv;
>   
>   	/* rxq's this binding is active on. */
>   	struct xarray bound_rxqs;
> diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
> index c15d8d4ca1f8..d3f3a91a6d93 100644
> --- a/net/core/netdev-genl.c
> +++ b/net/core/netdev-genl.c
> @@ -1044,13 +1044,11 @@ int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
>   		goto err_genlmsg_free;
>   	}
>   
> -	mutex_lock(&priv->lock);
> -
>   	err = 0;
>   	netdev = netdev_get_by_index_lock(genl_info_net(info), ifindex);
>   	if (!netdev) {
>   		err = -ENODEV;
> -		goto err_unlock_sock;
> +		goto err_genlmsg_free;
>   	}
>   	if (!netif_device_present(netdev))
>   		err = -ENODEV;
> @@ -1102,8 +1100,6 @@ int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
>   
>   	netdev_unlock(netdev);
>   
> -	mutex_unlock(&priv->lock);
> -
>   	return err < 0 ? err : 0;
>   
>   err_unbind:
> @@ -1112,8 +1108,6 @@ int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
>   	bitmap_free(rxq_bitmap);
>   err_unlock:
>   	netdev_unlock(netdev);
> -err_unlock_sock:
> -	mutex_unlock(&priv->lock);
>   err_genlmsg_free:
>   	nlmsg_free(rsp);
>   	return err;
> @@ -1185,12 +1179,10 @@ int netdev_nl_bind_tx_doit(struct sk_buff *skb, struct genl_info *info)
>   		goto err_genlmsg_free;
>   	}
>   
> -	mutex_lock(&priv->lock);
> -
>   	netdev = netdev_get_by_index_lock(genl_info_net(info), ifindex);
>   	if (!netdev) {
>   		err = -ENODEV;
> -		goto err_unlock_sock;
> +		goto err_genlmsg_free;
>   	}
>   
>   	if (!netif_device_present(netdev)) {
> @@ -1233,7 +1225,6 @@ int netdev_nl_bind_tx_doit(struct sk_buff *skb, struct genl_info *info)
>   	if (bind_dev != netdev)
>   		netdev_unlock(bind_dev);
>   	netdev_unlock(netdev);
> -	mutex_unlock(&priv->lock);
>   
>   	return genlmsg_reply(rsp, info);
>   
> @@ -1242,8 +1233,6 @@ int netdev_nl_bind_tx_doit(struct sk_buff *skb, struct genl_info *info)
>   		netdev_unlock(bind_dev);
>   err_unlock_netdev:
>   	netdev_unlock(netdev);
> -err_unlock_sock:
> -	mutex_unlock(&priv->lock);
>   err_genlmsg_free:
>   	nlmsg_free(rsp);
>   	return err;
> @@ -1418,19 +1407,17 @@ int netdev_nl_queue_create_doit(struct sk_buff *skb, struct genl_info *info)
>   
>   void netdev_nl_sock_priv_init(struct netdev_nl_sock *priv)
>   {
> -	INIT_LIST_HEAD(&priv->bindings);
> -	mutex_init(&priv->lock);
> +	xa_init(&priv->bindings);
>   }
>   
>   void netdev_nl_sock_priv_destroy(struct netdev_nl_sock *priv)
>   {
>   	struct net_devmem_dmabuf_binding *binding;
> -	struct net_devmem_dmabuf_binding *temp;
>   	netdevice_tracker dev_tracker;
>   	struct net_device *dev;
> +	unsigned long xa_idx;
>   
> -	mutex_lock(&priv->lock);
> -	list_for_each_entry_safe(binding, temp, &priv->bindings, list) {
> +	xa_for_each(&priv->bindings, xa_idx, binding) {
>   		mutex_lock(&binding->lock);
>   		dev = binding->dev;
>   		if (!dev) {
> @@ -1446,7 +1433,7 @@ void netdev_nl_sock_priv_destroy(struct netdev_nl_sock *priv)
>   		netdev_unlock(dev);
>   		netdev_put(dev, &dev_tracker);
>   	}
> -	mutex_unlock(&priv->lock);
> +	xa_destroy(&priv->bindings);
>   }
>   
>   static int netdev_genl_netdevice_event(struct notifier_block *nb,