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Date: Wed, 11 Mar 2015 22:43:07 +0100
From: Marc Kleine-Budde <mkl@...gutronix.de>
To: "Ahmed S. Darwish" <darwish.07@...il.com>,
Olivier Sobrie <olivier@...rie.be>,
Oliver Hartkopp <socketcan@...tkopp.net>,
Wolfgang Grandegger <wg@...ndegger.com>,
Andri Yngvason <andri.yngvason@...el.com>
CC: Linux-CAN <linux-can@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/3] can: kvaser_usb: Fix tx queue start/stop
race conditions
On 03/11/2015 06:37 PM, Ahmed S. Darwish wrote:
> From: Ahmed S. Darwish <ahmed.darwish@...eo.com>
>
> 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.
>
> start_xmit() tx_acknowledge()
> ............ ................
> atomic_inc(&tx_urbs);
> if (atomic_read(&tx_urbs) >= 16) {
> URB completion IRQ!
> -->
> atomic_dec(&tx_urbs);
> netif_wake_queue();
> return;
> <--
> end of IRQ!
> 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 protection.
>
> Signed-off-by: Ahmed S. Darwish <ahmed.darwish@...eo.com>
> ---
> drivers/net/can/usb/kvaser_usb.c | 83 ++++++++++++++++++++++++----------------
> 1 file changed, 51 insertions(+), 32 deletions(-)
>
> changelog-v3: Added missing spin_lock_init(). With all kernel
> lock debugging options set, I've been running my test suite
> for an hour now without apparent problems in dmesg so far.
>
> changelog-v2: Put bugfix patch at the start of the series.
>
> diff --git a/drivers/net/can/usb/kvaser_usb.c b/drivers/net/can/usb/kvaser_usb.c
> index a316fa4..e97a08c 100644
> --- a/drivers/net/can/usb/kvaser_usb.c
> +++ b/drivers/net/can/usb/kvaser_usb.c
> @@ -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);
I think it should be possible to move tun unlock before waking up the queue?
> }
>
> 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);
Same here?
>
> - 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;
>
Marc
--
Pengutronix e.K. | Marc Kleine-Budde |
Industrial Linux Solutions | Phone: +49-231-2826-924 |
Vertretung West/Dortmund | Fax: +49-5121-206917-5555 |
Amtsgericht Hildesheim, HRA 2686 | http://www.pengutronix.de |
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