Re: [PATCH net] xsk: freeze deferred pool teardown without blocking unregister

[netdev-bot+sashiko@kernel.org]

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- [Medium] The patch adds one global list, xsk_dev_pools
  (net/xdp/xsk_buff_pool.c), that holds every assigned XSK buffer pool…

--

xsk: freeze deferred pool teardown without blocking unregister

This moves deferred XSK buffer pool destruction from system_wq to
system_freezable_wq, so ndo_bpf() is not called on a suspended device. It
also adds a global list of assigned pools. NETDEV_UNREGISTER uses that
list to detach pools whose sockets have already left net->xdp.list.

> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index 33475b180ea6f..a2ae0e10d8933 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -2145,6 +2145,10 @@ static int xsk_notifier(struct notifier_block *this,
>  			mutex_unlock(&xs->mutex);
>  		}
>  		mutex_unlock(&net->xdp.lock);
> +		/* A released socket is no longer on xdp.list. Its pool can still
> +		 * hold a device reference on the frozen release workqueue.
> +		 */
> +		xp_clear_dev_all(dev);
>  		break;
>  	}
>  	return NOTIFY_DONE;
> diff --git a/net/xdp/xsk_buff_pool.c b/net/xdp/xsk_buff_pool.c
> index 9d2d94f1fb759..b5fd0850db5bb 100644
> --- a/net/xdp/xsk_buff_pool.c
> +++ b/net/xdp/xsk_buff_pool.c
> @@ -12,6 +12,11 @@
>  
>  #define ETH_PAD_LEN (ETH_HLEN + 2 * VLAN_HLEN  + ETH_FCS_LEN)
>  
> +/* Socket removal precedes the final pool put. Keep assigned pools visible to
> + * NETDEV_UNREGISTER even while their release work is waiting for process thaw.
> + */
> +static LIST_HEAD(xsk_dev_pools);
> +

[ ... ]

> +void xp_clear_dev_all(struct net_device *dev)
> +{
> +	struct xsk_buff_pool *pool, *next;
> +
> +	ASSERT_RTNL();
> +	list_for_each_entry_safe(pool, next, &xsk_dev_pools, dev_list)
> +		if (pool->netdev == dev)
> +			xp_clear_dev(pool);
> +}

[Severity: Medium]
Should xsk_dev_pools be scoped per netns or per netdev, rather than being
one global list?

As written, xsk_dev_pools holds every assigned pool from every network
namespace. xsk_notifier()->xp_clear_dev_all() walks the whole list under
RTNL on every NETDEV_UNREGISTER, in any namespace.

Before this patch, the notifier only walked net->xdp.list of the namespace
that owns the device. With this change, each unregister costs O(total pools
in the system). A batched unregister, such as netns teardown, costs
O(devices x global pools), all while RTNL is held.

xsk_create() only checks ns_capable(net->user_ns, CAP_NET_RAW). A user
inside a user namespace can therefore create many pools, for example with
copy-mode binds to veth or dummy queues, or with XDP_SHARED_UMEM backing
many pools from one umem. That would lengthen RTNL hold times during device
and netns teardown in unrelated namespaces.

Would tracking the pools per netdev or per netns limit the walk to pools
that can actually match dev?

>  static void xp_release_deferred(struct work_struct *work)
>  {
>  	struct xsk_buff_pool *pool = container_of(work, struct xsk_buff_pool,

-- 
Sashiko AI review · https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260930-xsk-suspend-teardown-v1-1-a6cac8c030be%40gmail.com