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

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Date:	Thu, 07 Jan 2010 10:05:37 -0500
From:	Michael Breuer <mbreuer@...jas.com>
To:	Jarek Poplawski <jarkao2@...il.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 1/7/2010 2:55 AM, 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.
>
>>> With this set and mtu=1500 all seems good - decent if not stellar
>>> throughput; no logged errors; no reported packet loss. As before, will
>>> leave running and see if anything falls apart.
>> Good news!
>>
>> Jarek P.
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>
Bad news - crashed about an hour after I wrote this email - under load - 
same crash as before. Network watchdog... lots of attempts to reset the 
adapter... then hw watchdog rebooted the system.
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