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

On Mon, Aug 10, 2026 at 12:48 PM Nikolay Aleksandrov
[off-list ref] wrote:

On 10/08/2026 09:57, Shivaji Kant wrote:

quoted

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 <redacted>
Signed-off-by: Shivaji Kant <redacted>
---
  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.

Ack, I will correct this in v2.

quoted

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.

Ack, will follow this consistent style.

quoted

+     }

      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,