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SubjectRe: Request for net guru help: waitqueue oops
Hans Grobler wrote:
>
> On Tue, 3 Oct 2000, Petko Manolov wrote:
>
> > It seems you're trying to sleep without process context (most likely in
> > net_tx_action). It would be more clear if you send that part of the
> > code.
>
> Since I don't explictly sleep anywhere, I'm not sure which code fragment
> would be useful... (net_tx_action is part of the networking layers). Which
> network functions can sleep (netif_rx, netif_stop_queue, netif_wake_queue,
> ...) ?


None of these can sleep. netif_*_queue routines are quite simple.
They are all atomic so there is no need to protect them with locks.


> After reading the softnet HOWTO, and some of the network drivers, I
> was unsure about the netif_stop_queue and netif_wake_queue functions. The
> howto indicated that these two should be protected from concurrent
> execution by a private lock. Not all the drivers seem to do this. In my
> case (although I'm running UP at the moment), I've used a driver global
> spinlock, for example:
>
> spinlock_t driver_lock = SPIN_LOCK_UNLOCKED;
>
> int scc72_hard_xmit (struct sk_buff *skb, struct net_device *dev)
> {
> unsigned long flags;
>
> /* ... */
>
> spin_lock_irqsave (&driver_lock, flags);
> netif_stop_queue (dev);
> spin_unlock_irqrestore (&driver_lock, flags);
>
> /* ... */
> }
>
> /* Example timer callback, to wake the queue */
> void scc72_interframewait (unsigned long channel)
> {
> unsigned long flags;
> struct scc72_channel *scc = (struct scc72_channel *) channel;
>
> /* ... */
>
> spin_lock_irqsave (&driver_lock, flags);
>
> /* ... */
>
> if (netif_queue_stopped (scc->dev))
> netif_wake_queue (scc->dev);
>
> spin_unlock_irqrestore (&driver_lock, flags);
> }


It is not clear from the example above if it is needed to lock in
the timer routine and what is locked inside. Anyway be careful
about locking regions shared between interrupts/bottom halves and
user context as this happens often.




best,
Petkan
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