Re: [PATCH v4 07/11] wifi: rtw88: Add common USB chip support

From: Sascha Hauer <s.hauer@pengutronix.de>
To: Ping-Ke Shih <pkshih@realtek.com>
Cc: "linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>,
	Neo Jou <neojou@gmail.com>, Hans Ulli Kroll <linux@ulli-kroll.de>,
	Yan-Hsuan Chuang <tony0620emma@gmail.com>,
	Kalle Valo <kvalo@kernel.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Martin Blumenstingl <martin.blumenstingl@googlemail.com>,
	"kernel@pengutronix.de" <kernel@pengutronix.de>,
	Johannes Berg <johannes@sipsolutions.net>,
	Alexander Hochbaum <alex@appudo.com>, Da Xue <da@libre.computer>,
	Bernie Huang <phhuang@realtek.com>,
	Viktor Petrenko <g0000ga@gmail.com>,
	neo_jou <neo_jou@realtek.com>
Subject: Re: [PATCH v4 07/11] wifi: rtw88: Add common USB chip support
Date: Wed, 30 Nov 2022 09:13:23 +0100	[thread overview]
Message-ID: <20221130081323.GE29728@pengutronix.de> (raw)
In-Reply-To: <4eee82341ef84d4aa063edeb6f23a70d@realtek.com>

On Wed, Nov 30, 2022 at 01:40:36AM +0000, Ping-Ke Shih wrote:
> 
> 
> > -----Original Message-----
> > From: Sascha Hauer <s.hauer@pengutronix.de>
> > Sent: Tuesday, November 29, 2022 6:08 PM
> > To: linux-wireless@vger.kernel.org
> > Cc: Neo Jou <neojou@gmail.com>; Hans Ulli Kroll <linux@ulli-kroll.de>; Ping-Ke Shih <pkshih@realtek.com>;
> > Yan-Hsuan Chuang <tony0620emma@gmail.com>; Kalle Valo <kvalo@kernel.org>; netdev@vger.kernel.org;
> > linux-kernel@vger.kernel.org; Martin Blumenstingl <martin.blumenstingl@googlemail.com>;
> > kernel@pengutronix.de; Johannes Berg <johannes@sipsolutions.net>; Alexander Hochbaum <alex@appudo.com>;
> > Da Xue <da@libre.computer>; Bernie Huang <phhuang@realtek.com>; Viktor Petrenko <g0000ga@gmail.com>;
> > Sascha Hauer <s.hauer@pengutronix.de>; neo_jou <neo_jou@realtek.com>
> > Subject: [PATCH v4 07/11] wifi: rtw88: Add common USB chip support
> > 
> > Add the common bits and pieces to add USB support to the RTW88 driver.
> > This is based on https://github.com/ulli-kroll/rtw88-usb.git which
> > itself is first written by Neo Jou.
> > 
> > Signed-off-by: neo_jou <neo_jou@realtek.com>
> > Signed-off-by: Hans Ulli Kroll <linux@ulli-kroll.de>
> > Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
> > ---
> 
> > +static void rtw_usb_write_port_tx_complete(struct urb *urb)
> > +{
> > +	struct rtw_usb_txcb *txcb = urb->context;
> > +	struct rtw_dev *rtwdev = txcb->rtwdev;
> > +	struct ieee80211_hw *hw = rtwdev->hw;
> > +	int max_iter = RTW_USB_MAX_XMITBUF_SZ;
> > +
> > +	while (true) {
> > +		struct sk_buff *skb = skb_dequeue(&txcb->tx_ack_queue);
> > +		struct ieee80211_tx_info *info;
> > +		struct rtw_usb_tx_data *tx_data;
> > +
> > +		if (!skb)
> > +			break;
> > +
> > +		if (!--max_iter) {
> 
> Don't you need to free 'skb'? or you should not dequeue skb in this situation?

My first reaction here was to call skb_queue_purge(), but that is
implemented as:

	while ((skb = skb_dequeue(list)) != NULL)
		kfree_skb(skb);

So basically it brings us into the same endless loop we are trying to
break out here.

If it was me I would just remove this check. *txcb is allocated once
in rtw_usb_tx_agg_skb(), &txcb->tx_ack_queue is added the number of skbs
that fit into RTW_USB_MAX_XMITBUF_SZ and here we dequeue these skbs
again. No other code even has the pointer to add skbs to this queue
concurrently.

Sascha

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