Re: [PATCH v2 3/7] [PATCH 3/8] can: CAN Network device driver and Netlink interface

Oliver Hartkopp
2009-05-13T10:10:36Z

Andrew Morton wrote:
> On Tue, 12 May 2009 11:28:00 +0200 Wolfgang Grandegger <wg@grandegger.com> wrote:
>
>
>> +int can_restart_now(struct net_device *dev)
>> +{
>> + struct can_priv *priv = netdev_priv(dev);
>> + struct net_device_stats *stats = &dev->stats;
>> + struct sk_buff *skb;
>> + struct can_frame *cf;
>> + int err;
>> +
>> + /* Synchronize with dev->hard_start_xmit() */
>> + netif_tx_lock(dev);
>> +
>> + /* Ensure that no more messages can go out */
>> + if (netif_carrier_ok(dev))
>> + netif_carrier_off(dev);
>> +
>> + /* Ensure that no more messages can come in */
>> + err = priv->do_set_mode(dev, CAN_MODE_STOP);
>> + if (err)
>> + return err;
>> +
>> + /* Now it's save to clean up */
>> + del_timer_sync(&priv->restart_timer);
>>
>
> This is deadlockable.
>
> It calls del_timer_sync() while holding netif_tx_lock(). But the timer
> handler (can_restart_now()) also takes netif_tx_lock(). So if the
> timer handler is presently running, it's sitting there spinning in
> netif_tx_lock(). And del_timer_sync() is sitting there waiting for the
> timer handler to complete.
>
>
>

Hi Wolfgang,

would it be an appropriate solution, just to invoke

netif_stop_queue() in can_bus_off()

and invoke

netif_wake_queue() in can_restart_now()

???

In a BUSOFF condition we're not able to send CAN frames anyway, so we
can disable the device queue and the we won't need any netif_tx_lock()
right?

AFAIK this was the original implementation before some of the latest
improvement with the netif_carrier stuff.

What do you think?

Best regards,
Oliver