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