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Date: Wed, 25 Mar 2009 20:20:50 -0700 (PDT) From: David Miller <davem@...emloft.net> To: herbert@...dor.apana.org.au Cc: jarkao2@...il.com, mingo@...e.hu, r.schwebel@...gutronix.de, torvalds@...ux-foundation.org, blaschka@...ux.vnet.ibm.com, tglx@...utronix.de, a.p.zijlstra@...llo.nl, linux-kernel@...r.kernel.org, kernel@...gutronix.de Subject: Re: Revert "gro: Fix legacy path napi_complete crash", From: Herbert Xu <herbert@...dor.apana.org.au> Date: Thu, 26 Mar 2009 10:41:29 +0800 > On Wed, Mar 25, 2009 at 11:54:56PM +0100, Jarek Poplawski wrote: > > > > 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... > > Yes this is why my original patch that started all this is broken. > However, this doesn't apply to my patch that open-codes __napi_complete. There is still a difference compared to your fix Herbert. Jarek's patch flushes GRO first before the unlink. I still believe that's critical, although like you I can't pinpoint why. I know that GRO ought to be disabled here, but what if for some reason it isn't? :-) Adam Richter has successfully tested Jarek's variant, and if Ingo's tests show that it makes his problem go away too then I'm definitely going with Jarek's patch. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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