Subject: Re: [RFC] net: napi fix

From: Jarek Poplawski <[email-masked]>
Date: Thu, 13 Dec 2007 14:49:53 +0100

On 12-12-2007 19:41, Kok, Auke wrote:
> David Miller wrote:
>> From: Andrew Gallatin <[email-masked]>
>> 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.