netdev - Re: [PATCH] sky2: Avoid race in sky2_change

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Message-Id: <20100503.163612.37225591.davem@davemloft.net>
Date:	Mon, 03 May 2010 16:36:12 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	shemminger@...tta.com
Cc:	mikem@...g3k.org, netdev@...r.kernel.org
Subject: Re: [PATCH] sky2: Avoid race in sky2_change_mtu

From: Stephen Hemminger <shemminger@...tta.com>
Date: Mon, 3 May 2010 16:26:34 -0700

> On Mon, 03 May 2010 23:18:56 +0900
> Mike McCormack <mikem@...g3k.org> wrote:
> 
>> netif_stop_queue does not ensure all in-progress transmits are complete,
>>  so use netif_tx_disable() instead.
>> 
>> Make sure NAPI polls are disabled, otherwise NAPI might trigger a TX
>>  restart between when we stop the queue and NAPI is disabled.
> 
> How could NAPI trigger a TX restart? Restart is a timer, not controlled
> by NAPI. There is a different race that your patch isn't covering.

I think he meant to say that NAPI can trigger a TX queue wake, which
indeed it can, and it will if there is space in the TX queue and
we happen to see the TXIDLE status at this time.
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