netdev - Re: [PATCH 1/3] virtio: fix virtio

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Message-ID: <4852D10E.40001@garzik.org>
Date:	Fri, 13 Jun 2008 15:57:02 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Mark McLoughlin <markmc@...hat.com>
CC:	Rusty Russell <rusty@...tcorp.com.au>, netdev@...r.kernel.org,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH 1/3] virtio: fix virtio_net xmit of freed skb bug

Mark McLoughlin wrote:
> On Thu, 2008-05-29 at 16:34 +1000, Rusty Russell wrote:
>> On Tuesday 27 May 2008 21:06:26 Mark McLoughlin wrote:
>>> On Mon, 2008-05-26 at 17:42 +1000, Rusty Russell wrote:
>>>> If we fail to transmit a packet, we assume the queue is full and put
>>>> the skb into last_xmit_skb.  However, if more space frees up before we
>>>> xmit it, we loop, and the result can be transmitting the same skb twice.
>>>>
>>>> Fix is simple: set skb to NULL if we've used it in some way, and check
>>>> before sending.
>> Great! It's a corner case, but it's no more complicated to do it your way.
>>
>> Minor mod, I find it clearer to have the vi->last_xmit_skb = NULL; under
>> the branch:
>>
>> Subject: [PATCH] virtio_net: Delay dropping tx skbs
>> Date: Tue, 27 May 2008 12:06:26 +0100
>> From: Mark McLoughlin <markmc@...hat.com>
>>
>> Currently we drop the skb in start_xmit() if we have a
>> queued buffer and fail to transmit it.
>>
>> However, if we delay dropping it until we've stopped the
>> queue and enabled the tx notification callback, then there
>> is a chance space might become available for it.
> 
> Hmm, we lost this one somewhere along the way ...

can someone resend?


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