From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Ahmed S. Darwish" Subject: [PATCH v3 1/3] can: kvaser_usb: Fix tx queue start/stop race conditions Date: Wed, 11 Mar 2015 13:37:44 -0400 Message-ID: <20150311173744.GA13095@linux> References: <20150226152011.GA6075@linux> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20150226152011.GA6075@linux> Sender: linux-kernel-owner@vger.kernel.org To: Olivier Sobrie , Oliver Hartkopp , Wolfgang Grandegger , Marc Kleine-Budde , Andri Yngvason Cc: Linux-CAN , LKML List-Id: linux-can.vger.kernel.org From: Ahmed S. Darwish 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 --- 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 #include #include #include @@ -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; -- 1.9.1