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

David Miller
2009-03-26T00:10:41Z

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

Ingo, in case it isn't completely obvious, it would be
wonderful if you could try Jarek's patch below with your
test case.

Thanks!

> 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...
>
> Jarek P.
> --- (2.6.29)
> net/core/dev.c | 6 +++++-
> 1 files changed, 5 insertions(+), 1 deletions(-)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index e3fe5c7..cf53c24 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -2589,7 +2589,11 @@ static int process_backlog(struct napi_struct *napi, int quota)
> skb = __skb_dequeue(&queue->input_pkt_queue);
> if (!skb) {
> local_irq_enable();
> - napi_complete(napi);
> + napi_gro_flush(napi);
> + local_irq_disable();
> + if (skb_queue_empty(&queue->input_pkt_queue))
> + __napi_complete(napi);
> + local_irq_enable();
> goto out;
> }
> local_irq_enable();