[PATCH net-next v2] net: convert netdev_nl_sock bindings list to xarray

[Shivaji Kant <shivajikant@google.com>]

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@google.com>
Signed-off-by: Shivaji Kant <shivajikant@google.com>
---
v1 -> v2:
  - Add explicit err_erase_dmabuf_bindings err label in net_devmem_bind_dmabuf()
    to align cleanup paths with the rest of the function (feedback from reviewer).

v1: https://lore.kernel.org/all/20260810065759.3735934-1-shivajikant@google.com/

 include/net/netdev_netlink.h |  5 ++---
 net/core/devmem.c            | 14 +++++++++++---
 net/core/devmem.h            |  4 ++--
 net/core/netdev-genl.c       | 25 ++++++-------------------
 4 files changed, 21 insertions(+), 27 deletions(-)

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..bdf8a0799a42 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) {
@@ -325,10 +326,17 @@ 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);
+		goto err_erase_dmabuf_bindings;
+	}
 
 	return binding;
 
+err_erase_dmabuf_bindings:
+	xa_erase(&net_devmem_dmabuf_bindings, binding->id);
 err_free_chunks:
 	gen_pool_for_each_chunk(binding->chunk_pool,
 				net_devmem_dmabuf_free_chunk_owner, NULL);
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,
-- 
2.55.0.654.g21b8a5bc05-goog