linux-kernel - Re: [PATCH] staging: rtl8192u: fix rmmod warn when wlan0 is renamed

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Message-ID: <20220718120149.GD2338@kadam>
Date:   Mon, 18 Jul 2022 15:01:49 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Tong Zhang <ztong0001@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Colin Ian King <colin.king@...el.com>,
        Saurav Girepunje <saurav.girepunje@...il.com>,
        Johan Hovold <johan@...nel.org>, linux-kernel@...r.kernel.org,
        linux-staging@...ts.linux.dev, Zheyu Ma <zheyuma97@...il.com>
Subject: Re: [PATCH] staging: rtl8192u: fix rmmod warn when wlan0 is renamed

On Sun, Jul 17, 2022 at 12:01:57AM -0700, Tong Zhang wrote:
> +static int rtl8192_usb_netdev_event(struct notifier_block *nb, unsigned long event,
> +		void *data)
> +{
> +	struct net_device *netdev = netdev_notifier_info_to_dev(data);
> +
> +	if (netdev->netdev_ops != &rtl8192_netdev_ops)
> +		goto out;
> +
> +	switch (event) {
> +		case NETDEV_CHANGENAME:
> +			rtl8192_debugfs_rename(netdev);
> +			break;
> +
> +		default:
> +			break;
> +	}

This isn't indented properly.  Don't forget to run ./scripts/checkpatch.pl
on your patch.

> +
> +out:
> +	return NOTIFY_DONE;
> +}
> +
> +static struct notifier_block rtl8192_usb_netdev_notifier = {
> +	.notifier_call = rtl8192_usb_netdev_event,
> +};
> +
> +

Here too.

>  static int __init rtl8192_usb_module_init(void)
>  {
>  	int ret;
> @@ -4788,10 +4638,14 @@ static int __init rtl8192_usb_module_init(void)

[ snip ]

> +void rtl8192_debugfs_init(struct net_device *dev)
> +{
> +	struct dentry *dir;
> +	struct r8192_priv *priv = (struct r8192_priv *)ieee80211_priv(dev);
> +
> +	dir = debugfs_create_dir(dev->name, NULL);
> +	if (IS_ERR_OR_NULL(dir))
> +		return;

In olden times the debugfs_create_dir() function used to return a mix
of error pointers and NULL.  But the idea with that function is that
most people are not supposed to check for errors.  But instead of that
they added all kind of *buggy* checks.  So then we made it just return
error pointers.

This code *does* care about it because it uses the
priv->debugfs_dir->d_name.name in rtl8192_debugfs_rename().

But caring about the debugfs dir and creating a rtl8192_debugfs_rename()
function is really unusual.  And normally when we have to do something
unusual that means we are doing something wrong...  :/

Anyway, just check for if (IS_ERR(dir)) {

> +
> +	debugfs_create_file("stats-rx", 0444, dir, dev, &rtl8192_usb_stats_rx_fops);
> +	debugfs_create_file("stats-tx", 0444, dir, dev, &rtl8192_usb_stats_tx_fops);
> +	debugfs_create_file("stats-ap", 0444, dir, dev, &rtl8192_usb_stats_ap_fops);
> +	debugfs_create_file("registers", 0444, dir, dev, &rtl8192_usb_registers_fops);
> +
> +	priv->debugfs_dir = dir;
> +}
> +
> +void rtl8192_debugfs_exit(struct net_device *dev)
> +{
> +	struct r8192_priv *priv = (struct r8192_priv *)ieee80211_priv(dev);
> +	if (!priv->debugfs_dir)
> +		return;
> +	debugfs_remove_recursive(priv->debugfs_dir);
> +	priv->debugfs_dir = NULL;
> +}
> +
> +void rtl8192_debugfs_rename(struct net_device *dev)
> +{
> +	struct r8192_priv *priv = (struct r8192_priv *)ieee80211_priv(dev);
> +
> +	if (!priv->debugfs_dir)
> +		return;
> +
> +	if (!strcmp(priv->debugfs_dir->d_name.name, dev->name))
> +		return;
> +
> +	debugfs_rename(priv->debugfs_dir->d_parent, priv->debugfs_dir,
> +			priv->debugfs_dir->d_parent, dev->name);
> +}
> +

regards,
dan carpenter