netdev - Re: [PATCH v3] net: Add mhi-net driver

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Date:   Thu, 15 Oct 2020 09:25:56 +0200
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Loic Poulain <loic.poulain@...aro.org>, davem@...emloft.net,
        kuba@...nel.org
Cc:     netdev@...r.kernel.org, hemantk@...eaurora.org,
        manivannan.sadhasivam@...aro.org
Subject: Re: [PATCH v3] net: Add mhi-net driver



On 10/14/20 1:53 PM, Loic Poulain wrote:
> This patch adds a new network driver implementing MHI transport for
> network packets. Packets can be in any format, though QMAP (rmnet)
> is the usual protocol (flow control + PDN mux).
> 

...

> +static void mhi_net_rx_refill_work(struct work_struct *work)
> +{
> +	struct mhi_net_dev *mhi_netdev = container_of(work, struct mhi_net_dev,
> +						      rx_refill.work);
> +	struct net_device *ndev = mhi_netdev->ndev;
> +	struct mhi_device *mdev = mhi_netdev->mdev;
> +	struct sk_buff *skb;
> +	int err;
> +
> +	do {
> +		skb = netdev_alloc_skb(ndev, READ_ONCE(ndev->mtu));
> +		if (unlikely(!skb))
> +			break;

It is a bit strange you use READ_ONCE(ndev->mtu) here, but later
re-read ndev->mtu

It seems you need to store the READ_ONCE() in a temporary variable,

                unsigned int mtu = READ_ONCE(ndev->mtu);

> +
> +		err = mhi_queue_skb(mdev, DMA_FROM_DEVICE, skb, ndev->mtu,
> +				    MHI_EOT);

                 s/ndev->mtu/mtu/


> +		if (err) {
> +			if (unlikely(err != -ENOMEM))
> +				net_err_ratelimited("%s: Failed to queue RX buf (%d)\n",
> +						    ndev->name, err);
> +			kfree_skb(skb);
> +			break;
> +		}
> +
> +		atomic_inc(&mhi_netdev->stats.rx_queued);

This is an unbound loop in the kernel ?

Please add a :

		cond_resched();

Before anyone gets hurt.


> +	} while (1);
> +
> +	/* If we're still starved of rx buffers, reschedule latter */
> +	if (unlikely(!atomic_read(&mhi_netdev->stats.rx_queued)))
> +		schedule_delayed_work(&mhi_netdev->rx_refill, HZ / 2);
> +}
> +
>