netdev - Re: [PATCH net-next v11 10/21] net: add helpers for setting a memory provider on an rx queue

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Message-ID: <20250116182558.4c7b66f6@kernel.org>
Date: Thu, 16 Jan 2025 18:25:58 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: David Wei <dw@...idwei.uk>
Cc: io-uring@...r.kernel.org, netdev@...r.kernel.org, Jens Axboe
 <axboe@...nel.dk>, Pavel Begunkov <asml.silence@...il.com>, Paolo Abeni
 <pabeni@...hat.com>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Jesper Dangaard Brouer <hawk@...nel.org>, David
 Ahern <dsahern@...nel.org>, Mina Almasry <almasrymina@...gle.com>,
 Stanislav Fomichev <stfomichev@...il.com>, Joe Damato <jdamato@...tly.com>,
 Pedro Tammela <pctammela@...atatu.com>
Subject: Re: [PATCH net-next v11 10/21] net: add helpers for setting a
 memory provider on an rx queue

On Thu, 16 Jan 2025 15:16:52 -0800 David Wei wrote:
> +static void __net_mp_close_rxq(struct net_device *dev, unsigned ifq_idx,
> +			      struct pp_memory_provider_params *old_p)
> +{
> +	struct netdev_rx_queue *rxq;
> +	int ret;
> +
> +	if (WARN_ON_ONCE(ifq_idx >= dev->real_num_rx_queues))
> +		return;
> + 
> +	rxq = __netif_get_rx_queue(dev, ifq_idx);

I think there's a small race between io_uring closing and the netdev
unregister. We can try to uninstall twice, let's put

	/* Callers holding a netdev ref may get here after we already
	 * went thru shutdown via dev_memory_provider_uninstall().
	 */
	if (dev->reg_state > NETREG_REGISTERED &&
	    !rxq->mp_params.mp_ops)
		return;

here, and in dev_memory_provider_uninstall() clear the pointers?

> +	if (WARN_ON_ONCE(rxq->mp_params.mp_ops != old_p->mp_ops ||
> +			 rxq->mp_params.mp_priv != old_p->mp_priv))
> +		return;
> +
> +	rxq->mp_params.mp_ops = NULL;
> +	rxq->mp_params.mp_priv = NULL;
> +	ret = netdev_rx_queue_restart(dev, ifq_idx);
> +	if (ret)
> +		pr_devel("Could not restart queue %u after removing memory provider.\n",
> +			 ifq_idx);
> +}