Date: Tue, 24 Mar 2009 19:09:14 -0700 (PDT)
Message-Id: <20090324.190914.117958201.davem@davemloft.net>
To: herbert@gondor.apana.org.au
Cc: mingo@elte.hu, r.schwebel@pengutronix.de, torvalds@linux-foundation.org,
       blaschka@linux.vnet.ibm.com, tglx@linutronix.de, a.p.zijlstra@chello.nl,
       linux-kernel@vger.kernel.org, kernel@pengutronix.de
Subject: Re: Revert "gro: Fix legacy path napi_complete crash",
From: David Miller <davem@davemloft.net>
In-Reply-To: <20090325003235.GC2297@gondor.apana.org.au>
References: <20090324155911.GA30824@gondor.apana.org.au>
	<20090324160241.GA11060@elte.hu>
	<20090325003235.GC2297@gondor.apana.org.au>
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From: Herbert Xu <herbert@gondor.apana.org.au>
Date: Wed, 25 Mar 2009 08:32:35 +0800

> On Tue, Mar 24, 2009 at 05:02:41PM +0100, Ingo Molnar wrote:
> > 
> > * Herbert Xu <herbert@gondor.apana.org.au> wrote:
> >
> > > What's the NIC and config on this one? If it's still using the 
> > > legacy/netif_rx path, where GRO is off by default, this patch 
> > > should make it exactly the same as with my original patch 
> > > reverted.
> > 
> > Same forcedeth box i reported before. Config below. (note: if you 
> > want to use it you need to run it through 'make oldconfig', with all 
> > defaults accepted)
> >
> > CONFIG_FORCEDETH=y
> > CONFIG_FORCEDETH_NAPI=y
> 
> This means that we shouldn't even invoke netif_rx/process_backlog,
> so something else is going on.

There is always loopback which does netif_rx().

Combine that with the straight NAPI receive that forcedeth
is doing here and I'm sure there are all kinds of race
scenerios possible :-)

You're right about GRO not being relevant here.  To be honest
I wouldn't be disappointed if GRO was simply on by default
even for the legacy paths.
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