Re: Revert "gro: Fix legacy path napi_complete crash",

David Miller
2009-03-26T00:04:20Z

From: Jarek Poplawski <jarkao2@gmail.com>
Date: Wed, 25 Mar 2009 23:54:56 +0100

> Herbert Xu wrote, On 03/25/2009 01:26 PM:
>
> > On Wed, Mar 25, 2009 at 01:20:46PM +0100, Ingo Molnar wrote:
> >> ok - i have started testing the delta below, on top of the plain
> >> revert.
> >
> > Thanks! BTW Ingo, any chance you could help us identify the problem
> > with the previous patch? I don't have a forcedeth machine here
> > and the hang you had with my patch that open-coded __napi_complete
> > appears intimately connected to forcedeth (with NAPI enabled).
>
> Of course it's too late for verifying this now, but (for the future)
> I think, this scenario could be considered:
>
> process_backlog() netif_rx()
>
> if (!skb)
> local_irq_enable()
> if (queue.qlen) //NO
> napi_schedule() //NOTHING
> __skb_queue_tail() //qlen > 0
> napi_complete()
> ... ...
> Every next netif_rx() sees
> qlen > 0, so napi is never
> scheduled again.
>
> Then, something like this might work...

Excellent detective work, I would have never figured this one
out.

Herbert can you take a good look at this can confirm Jarek's
findings?

Thanks!