netdev - Re: [PATCH] netpoll: fix race on poll_list resulting in garbage entry

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Message-ID: <20081211090104.02cab3d4@s6510>
Date:	Thu, 11 Dec 2008 09:01:04 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	Neil Horman <nhorman@...driver.com>, netdev@...r.kernel.org,
	davem@...emloft.net
Subject: Re: [PATCH] netpoll: fix race on poll_list resulting in garbage
 entry

On Thu, 11 Dec 2008 13:07:28 +0000
Jarek Poplawski <jarkao2@...il.com> wrote:

> On 09-12-2008 22:06, Neil Horman wrote:
> ...
> > When executing napi->poll from the netpoll_path, this bit will
> > be set. When a driver calls netif_rx_complete, if that bit is set, it will not
> > remove the napi_struct from the poll_list.  That work will be saved for the next
> > iteration of net_rx_action.
> 
> This could be not enough: some drivers, e.g. sky2, call napi_complete()
> directly.
> 

There is good reason for this. Although most drivers only have one NAPI
instance per device, and multiqueue drivers have several NAPI structures
per device, a few devices like sky2 need to support multiple devices
running off one NAPI receive. The Marvell hardware has a common receive
interrupt for both ports on a dual port card.

This kind of hardware limits usage of netpoll. Only one port can be
used with netpoll because netpoll makes assumptions about NAPI
association.
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