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    SubjectRe: Revert "gro: Fix legacy path napi_complete crash",
    From
    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!


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