netdev - Re: [PATCH net-next v5 2/2] mctp i2c: MCTP I2C binding driver

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Message-ID: <b857c3087443f86746d81c1d686eaf5044db98a7.camel@codeconstruct.com.au>
Date:   Tue, 15 Feb 2022 12:22:14 +0800
From:   Matt Johnston <matt@...econstruct.com.au>
To:     Jakub Kicinski <kuba@...nel.org>, Wolfram Sang <wsa@...nel.org>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jeremy Kerr <jk@...econstruct.com.au>,
        linux-i2c@...r.kernel.org, netdev@...r.kernel.org,
        Zev Weiss <zev@...ilderbeest.net>
Subject: Re: [PATCH net-next v5 2/2] mctp i2c: MCTP I2C binding driver

On Fri, 2022-02-11 at 14:38 -0800, Jakub Kicinski wrote:
> 
> > +// Removes and unregisters a mctp-i2c netdev
> > +static void mctp_i2c_free_netdev(struct mctp_i2c_dev *midev)
> > 
> You're doing a lot before the unregister call, this is likely racy.
> The usual flow is to unregister the netdev, then do uninit, then free.
> For instance you purge the queue but someone may Tx afterwards.
> needs_free_netdev is a footgun.

Thanks Jakub. I've reworked it here to do the work before register/after
unregister, without needs_free_netdev.

One question, the tx thread calls netif_wake_queue() - is it safe to call
that after unregister_netdev()? (before free_netdev)
I've moved the kthread_stop() to the post-unregister cleanup.

static int mctp_i2c_tx_thread(void *data)
{
	struct mctp_i2c_dev *midev = data;
	struct sk_buff *skb;
	unsigned long flags;

	for (;;) {
		if (kthread_should_stop())
			break;

		spin_lock_irqsave(&midev->tx_queue.lock, flags);
		skb = __skb_dequeue(&midev->tx_queue);
		if (netif_queue_stopped(midev->ndev))
			netif_wake_queue(midev->ndev);      // <-------
		spin_unlock_irqrestore(&midev->tx_queue.lock, flags);


> > +	INIT_LIST_HEAD(&mi_driver_state.clients);
> > +	mutex_init(&mi_driver_state.lock);
> 
> I think there are static initializers for these.
*nod*


Thanks,
Matt