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

[Oliver Hartkopp]

Wolfgang Grandegger wrote:
> Oliver Hartkopp wrote:
>   
> > Andrew Morton wrote:
> >     
> > > On Tue, 12 May 2009 11:28:00 +0200 Wolfgang Grandegger
> > > <wg@xxxxxxxxxxxxxx> 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?
> >     
>
> The problem is the "manual" restart triggered via the netlink interface,
> which can occur in the middle of ndo_start_xmit().
>
>   

Ah, i see.

What if the manual restart via netlink would also stop the queue and 
start the timer?

Regards,
Oliver

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