netdev - Re: [net-next.git 1/7] stmmac: review napi gro support

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Date:	Wed, 03 Apr 2013 06:39:34 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Giuseppe CAVALLARO <peppe.cavallaro@...com>
Cc:	netdev@...r.kernel.org
Subject: Re: [net-next.git 1/7] stmmac: review napi gro support

On Wed, 2013-04-03 at 09:41 +0200, Giuseppe CAVALLARO wrote:

> Hmm, I'm in trouble on this :-). Indeed I can understand the (fatal)
> race and why napi_complete should be used. Sorry! So my fault and this 
> patch has to be discarded. I don't understand why I have not seen any
> problems while running/stressing on SMP system. Have you got any idea?
> 

So because you don't hit the race on your machine and your tests, we can
remove all the needed spinlock() and various hard irq masking, and
introduce all sort of races ?

Try to use a combination of two NICS, and you'll hit the bug even on UP.

There is a single poll_list per cpu, and we insert new elements in this
list under hard irq.

So deleting elements _must_ be done under the protection of hard irq
masking.

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