linux-kernel - Re: [PATCH] af_packet: Don't use skb after dev_queue

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Message-ID: <20100107082140.GB7229@ff.dom.local>
Date:	Thu, 7 Jan 2010 08:21:40 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Michael Breuer <mbreuer@...jas.com>
Cc:	Stephen Hemminger <shemminger@...ux-foundation.org>,
	David Miller <davem@...emloft.net>, akpm@...ux-foundation.org,
	flyboy@...il.com, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH] af_packet: Don't use skb after dev_queue_xmit()

On Thu, Jan 07, 2010 at 02:55:20AM -0500, Michael Breuer wrote:
> On 1/7/2010 2:47 AM, Jarek Poplawski wrote:
>> On Thu, Jan 07, 2010 at 02:20:22AM -0500, Michael Breuer wrote:
>>    
>>> ...
>>> Reapplied a couple of earlier patches - still can't do jumbo frames, but
>>> the rx errors are gone and speed has improved. Too early to assure that
>>> it's stable.
>>>
>>> Patches that seem to fix the rx drops (all from Stephen):
>>> 1) Patch change to tx_init
>>> 2) Patch to lock netif_device_detach
>>> 3) Patch to sky2_tx_complete to add netif_device_present test
>>> Also in the mix: Jarek's alternative 2
>>>      
>> BTW, the main difference between alt. 1 and 2 is error notification:
>> alternative 2 doesn't hide some (most) of drops, so, dependending on
>> app, there might be more and faster retransmits. (I don't know what
>> apps used by you (other than dhcp) can depend so much on this.)
>>
>>    
> Unless I misread the code, I think that in some cases e skb is actually  
> freed if the cfq (among others perhaps) scheduler returns an error on  
> enqueue (flow control perhaps).  Thus with alternative 1, it is possible  
> that the skb is acted upon after being freed - this would be consistent  
> with the DMAR errors I saw.

I can't see your point: could you give some scenario?

Jarek P.
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