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can: kvaser_usb: Fix tx queue start/stop race conditions
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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: Ahmed S. Darwish <ahmed.darwish@valeo.com>
Cc: linux-stable <stable@vger.kernel.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
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@marckleinebudde
Ahmed S. Darwish authored and marckleinebudde committed Mar 14, 2015
1 parent 963a822 commit a9dc960
Showing 1 changed file with 51 additions and 32 deletions.
83 changes: 51 additions & 32 deletions drivers/net/can/usb/kvaser_usb.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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>
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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)
Expand Down Expand Up @@ -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)
Expand Down Expand Up @@ -1515,6 +1510,24 @@ static int kvaser_usb_open(struct net_device *netdev)
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;
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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) {
Expand All @@ -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;
Expand All @@ -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++;
Expand Down Expand Up @@ -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)
Expand All @@ -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;
Expand Down

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