Re: Revert "gro: Fix legacy path napi_complete crash", (was: Re: Linux 2.6.29)

Sascha Hauer
2009-03-24T15:31:01Z

On Tue, Mar 24, 2009 at 11:09:28PM +0800, Herbert Xu wrote:
> On Tue, Mar 24, 2009 at 03:39:42PM +0100, Ingo Molnar wrote:
> >
> > Subject: [PATCH] net: Fix netpoll lockup in legacy receive path
>
> Actually, this patch is still racy. If some interrupt comes in
> and we suddenly get the maximum amount of backlog we can still
> hang when we call __napi_complete incorrectly. It's unlikely
> but we certainly shouldn't allow that. Here's a better version.

Yes, this one works. I always wanted to give a

Tested-by: Sascha Hauer <s.hauer@pengutronix.de>

Thanks
Sascha

>
> net: Fix netpoll lockup in legacy receive path
>
> When I fixed the GRO crash in the legacy receive path I used
> napi_complete to replace __napi_complete. Unfortunately they're
> not the same when NETPOLL is enabled, which may result in us
> not calling __napi_complete at all.
>
> What's more, we really do need to keep the __napi_complete call
> within the IRQ-off section since in theory an IRQ can occur in
> between and fill up the backlog to the maximum, causing us to
> lock up.
>
> This patch fixes this by essentially open-coding __napi_complete.
>
> Note we no longer need the memory barrier because this function
> is per-cpu.
>
> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index e3fe5c7..2a7f6b3 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -2588,9 +2588,10 @@ static int process_backlog(struct napi_struct *napi, int quota)
> local_irq_disable();
> skb = __skb_dequeue(&queue->input_pkt_queue);
> if (!skb) {
> + list_del(&napi->poll_list);
> + clear_bit(NAPI_STATE_SCHED, &napi->state);
> local_irq_enable();
> - napi_complete(napi);
> - goto out;
> + break;
> }
> local_irq_enable();
>
> @@ -2599,7 +2600,6 @@ static int process_backlog(struct napi_struct *napi, int quota)
>
> napi_gro_flush(napi);
>
> -out:
> return work;
> }
>
> Thanks,
> --
> Visit Openswan at http://www.openswan.org/
> Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
> Home Page: http://gondor.apana.org.au/~herbert/
> PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
>

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