netdev - Re: [PATCH net-next v9 04/14] netdev: support binding dma-buf to netdevice

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Message-ID: <d85f4ba4-774f-4577-985f-45a5a1866da7@davidwei.uk>
Date: Sat, 18 May 2024 11:46:09 -0700
From: David Wei <dw@...idwei.uk>
To: Mina Almasry <almasrymina@...gle.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
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Subject: Re: [PATCH net-next v9 04/14] netdev: support binding dma-buf to
 netdevice

On 2024-05-10 16:21, Mina Almasry wrote:
> +void net_devmem_unbind_dmabuf(struct net_devmem_dmabuf_binding *binding)
> +{
> +	struct netdev_rx_queue *rxq;
> +	unsigned long xa_idx;
> +	unsigned int rxq_idx;
> +
> +	if (!binding)
> +		return;
> +
> +	if (binding->list.next)
> +		list_del(&binding->list);
> +
> +	xa_for_each(&binding->bound_rxq_list, xa_idx, rxq) {
> +		if (rxq->mp_params.mp_priv == binding) {
> +			/* We hold the rtnl_lock while binding/unbinding
> +			 * dma-buf, so we can't race with another thread that
> +			 * is also modifying this value. However, the page_pool
> +			 * may read this config while it's creating its
> +			 * rx-queues. WRITE_ONCE() here to match the
> +			 * READ_ONCE() in the page_pool.
> +			 */
> +			WRITE_ONCE(rxq->mp_params.mp_ops, NULL);
> +			WRITE_ONCE(rxq->mp_params.mp_priv, NULL);
> +
> +			rxq_idx = get_netdev_rx_queue_index(rxq);
> +
> +			netdev_rx_queue_restart(binding->dev, rxq_idx);

What if netdev_rx_queue_restart() fails? Depending on where it failed, a
queue might still be filled from struct net_devmem_dmabuf_binding. This
is one downside of the current situation with netdev_rx_queue_restart()
needing to do allocations each time.

Perhaps a full reset if individual queue restart fails?