Commit a9dc960c authored by Ahmed S. Darwish's avatar Ahmed S. Darwish Committed by Marc Kleine-Budde
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can: kvaser_usb: Fix tx queue start/stop race conditions 



A number of tx queue wake-up events went missing due to the
outlined scenario below. Start state is a pool of 16 tx URBs,
active tx_urbs count = 15, with the netdev tx queue open.

CPU #1 [softirq]                         CPU #2 [softirq]
start_xmit()                             tx_acknowledge()
................                         ................

atomic_inc(&tx_urbs);
if (atomic_read(&tx_urbs) >= 16) {
                        -->
                                         atomic_dec(&tx_urbs);
                                         netif_wake_queue();
                                         return;
                        <--
    netif_stop_queue();
}

At the end, the correct state expected is a 15 tx_urbs count
value with the tx queue state _open_. Due to the race, we get
the same tx_urbs value but with the tx queue state _stopped_.
The wake-up event is completely lost.

Thus avoid hand-rolled concurrency mechanisms and use a proper
lock for contexts and tx queue protection.

Signed-off-by: default avatarAhmed S. Darwish <ahmed.darwish@valeo.com>
Cc: linux-stable <stable@vger.kernel.org>
Signed-off-by: default avatarMarc Kleine-Budde <mkl@pengutronix.de>
parent 963a822b

drivers/net/can/usb/kvaser_usb.c

+51 −32
Original line number Diff line number Diff line
@@ -14,6 +14,7 @@ 
 * Copyright (C) 2015 Valeo S.A.

 */



#include <linux/spinlock.h>

#include <linux/kernel.h>

#include <linux/completion.h>

#include <linux/module.h>
@@ -467,10 +468,11 @@ struct kvaser_usb { 
struct kvaser_usb_net_priv {

	struct can_priv can;



	atomic_t active_tx_urbs;

	struct usb_anchor tx_submitted;

	spinlock_t tx_contexts_lock;

	int active_tx_contexts;

	struct kvaser_usb_tx_urb_context tx_contexts[MAX_TX_URBS];



	struct usb_anchor tx_submitted;

	struct completion start_comp, stop_comp;



	struct kvaser_usb *dev;
@@ -694,6 +696,7 @@ static void kvaser_usb_tx_acknowledge(const struct kvaser_usb *dev, 
	struct kvaser_usb_net_priv *priv;

	struct sk_buff *skb;

	struct can_frame *cf;

	unsigned long flags;

	u8 channel, tid;



	channel = msg->u.tx_acknowledge_header.channel;
@@ -737,12 +740,15 @@ static void kvaser_usb_tx_acknowledge(const struct kvaser_usb *dev, 


	stats->tx_packets++;

	stats->tx_bytes += context->dlc;

	can_get_echo_skb(priv->netdev, context->echo_index);



	context->echo_index = MAX_TX_URBS;

	atomic_dec(&priv->active_tx_urbs);

	spin_lock_irqsave(&priv->tx_contexts_lock, flags);



	can_get_echo_skb(priv->netdev, context->echo_index);

	context->echo_index = MAX_TX_URBS;

	--priv->active_tx_contexts;

	netif_wake_queue(priv->netdev);



	spin_unlock_irqrestore(&priv->tx_contexts_lock, flags);

}



static void kvaser_usb_simple_msg_callback(struct urb *urb)
@@ -803,17 +809,6 @@ static int kvaser_usb_simple_msg_async(struct kvaser_usb_net_priv *priv, 
	return 0;

}



static void kvaser_usb_unlink_tx_urbs(struct kvaser_usb_net_priv *priv)

{

	int i;



	usb_kill_anchored_urbs(&priv->tx_submitted);

	atomic_set(&priv->active_tx_urbs, 0);



	for (i = 0; i < MAX_TX_URBS; i++)

		priv->tx_contexts[i].echo_index = MAX_TX_URBS;

}



static void kvaser_usb_rx_error_update_can_state(struct kvaser_usb_net_priv *priv,

						 const struct kvaser_usb_error_summary *es,

						 struct can_frame *cf)
@@ -1515,6 +1510,24 @@ error: 
	return err;

}



static void kvaser_usb_reset_tx_urb_contexts(struct kvaser_usb_net_priv *priv)

{

	int i;



	priv->active_tx_contexts = 0;

	for (i = 0; i < MAX_TX_URBS; i++)

		priv->tx_contexts[i].echo_index = MAX_TX_URBS;

}



/* This method might sleep. Do not call it in the atomic context

 * of URB completions.

 */

static void kvaser_usb_unlink_tx_urbs(struct kvaser_usb_net_priv *priv)

{

	usb_kill_anchored_urbs(&priv->tx_submitted);

	kvaser_usb_reset_tx_urb_contexts(priv);

}



static void kvaser_usb_unlink_all_urbs(struct kvaser_usb *dev)

{

	int i;
@@ -1634,6 +1647,7 @@ static netdev_tx_t kvaser_usb_start_xmit(struct sk_buff *skb, 
	struct kvaser_msg *msg;

	int i, err, ret = NETDEV_TX_OK;

	u8 *msg_tx_can_flags = NULL;		/* GCC */

	unsigned long flags;



	if (can_dropped_invalid_skb(netdev, skb))

		return NETDEV_TX_OK;
@@ -1687,12 +1701,21 @@ static netdev_tx_t kvaser_usb_start_xmit(struct sk_buff *skb, 
	if (cf->can_id & CAN_RTR_FLAG)

		*msg_tx_can_flags |= MSG_FLAG_REMOTE_FRAME;



	spin_lock_irqsave(&priv->tx_contexts_lock, flags);

	for (i = 0; i < ARRAY_SIZE(priv->tx_contexts); i++) {

		if (priv->tx_contexts[i].echo_index == MAX_TX_URBS) {

			context = &priv->tx_contexts[i];



			context->echo_index = i;

			can_put_echo_skb(skb, netdev, context->echo_index);

			++priv->active_tx_contexts;

			if (priv->active_tx_contexts >= MAX_TX_URBS)

				netif_stop_queue(netdev);



			break;

		}

	}

	spin_unlock_irqrestore(&priv->tx_contexts_lock, flags);



	/* This should never happen; it implies a flow control bug */

	if (!context) {
@@ -1704,7 +1727,6 @@ static netdev_tx_t kvaser_usb_start_xmit(struct sk_buff *skb, 
	}



	context->priv = priv;

	context->echo_index = i;

	context->dlc = cf->can_dlc;



	msg->u.tx_can.tid = context->echo_index;
@@ -1716,18 +1738,17 @@ static netdev_tx_t kvaser_usb_start_xmit(struct sk_buff *skb, 
			  kvaser_usb_write_bulk_callback, context);

	usb_anchor_urb(urb, &priv->tx_submitted);



	can_put_echo_skb(skb, netdev, context->echo_index);



	atomic_inc(&priv->active_tx_urbs);



	if (atomic_read(&priv->active_tx_urbs) >= MAX_TX_URBS)

		netif_stop_queue(netdev);



	err = usb_submit_urb(urb, GFP_ATOMIC);

	if (unlikely(err)) {

		spin_lock_irqsave(&priv->tx_contexts_lock, flags);



		can_free_echo_skb(netdev, context->echo_index);

		context->echo_index = MAX_TX_URBS;

		--priv->active_tx_contexts;

		netif_wake_queue(netdev);



		spin_unlock_irqrestore(&priv->tx_contexts_lock, flags);



		atomic_dec(&priv->active_tx_urbs);

		usb_unanchor_urb(urb);



		stats->tx_dropped++;
@@ -1854,7 +1875,7 @@ static int kvaser_usb_init_one(struct usb_interface *intf, 
	struct kvaser_usb *dev = usb_get_intfdata(intf);

	struct net_device *netdev;

	struct kvaser_usb_net_priv *priv;

	int i, err;

	int err;



	err = kvaser_usb_send_simple_msg(dev, CMD_RESET_CHIP, channel);

	if (err)
@@ -1868,19 +1889,17 @@ static int kvaser_usb_init_one(struct usb_interface *intf, 


	priv = netdev_priv(netdev);



	init_usb_anchor(&priv->tx_submitted);

	init_completion(&priv->start_comp);

	init_completion(&priv->stop_comp);



	init_usb_anchor(&priv->tx_submitted);

	atomic_set(&priv->active_tx_urbs, 0);



	for (i = 0; i < ARRAY_SIZE(priv->tx_contexts); i++)

		priv->tx_contexts[i].echo_index = MAX_TX_URBS;



	priv->dev = dev;

	priv->netdev = netdev;

	priv->channel = channel;



	spin_lock_init(&priv->tx_contexts_lock);

	kvaser_usb_reset_tx_urb_contexts(priv);



	priv->can.state = CAN_STATE_STOPPED;

	priv->can.clock.freq = CAN_USB_CLOCK;

	priv->can.bittiming_const = &kvaser_usb_bittiming_const;

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