linux-kernel - Re: [RFC] net: napi fix

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Message-ID: <20071213134953.GA3806@ff.dom.local>
Date:	Thu, 13 Dec 2007 14:49:53 +0100
From:	Jarek Poplawski <jarkao2@...il.com>
To:	"Kok, Auke" <auke-jan.h.kok@...el.com>
Cc:	David Miller <davem@...emloft.net>, gallatin@...i.com,
	joonwpark81@...il.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, jgarzik@...ox.com,
	shemminger@...ux-foundation.org,
	Jesse Brandeburg <jesse.brandeburg@...el.com>
Subject: Re: [RFC] net: napi fix

On 12-12-2007 19:41, Kok, Auke wrote:
> David Miller wrote:
>> From: Andrew Gallatin <gallatin@...i.com>
>> Date: Wed, 12 Dec 2007 12:29:23 -0500
>>
>>> Is the netif_running() check even required?
>> No, it is not.
>>
>> When a device is brought down, one of the first things
>> that happens is that we wait for all pending NAPI polls
>> to complete, then block any new polls from starting.
> 
> I think this was previously (pre-2.6.24) not the case, which is why e1000 et al
> has this check as well and that's exactly what is causing most of the
> net_rx_action oopses in the first place. Without the netif_running() check
> previously the drivers were just unusable with NAPI and prone to many races with
> down (i.e. touching some ethtool ioctl which wants to do a reset while routing
> small packets at high numbers). that's why we added the netif_running() check in
> the first place :)
> 
> There might be more drivers lurking that need this change...
> 

As a matter of fact, since it's "unlikely()" in net_rx_action() anyway,
I wonder what is the main reason or gain of leaving such a tricky
exception, instead of letting drivers to always decide which is the
best moment for napi_complete()? (Or maybe even, in such a case, they
should call some function with this list_move_tail() if it's so
useful?)

Regards,
Jarek P.
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