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Date: Fri, 12 Dec 2008 07:18:35 -0500 From: Neil Horman <nhorman@...driver.com> To: Stephen Hemminger <shemminger@...tta.com> Cc: Jarek Poplawski <jarkao2@...il.com>, netdev@...r.kernel.org, davem@...emloft.net Subject: Re: [PATCH] netpoll: fix race on poll_list resulting in garbage entry On Thu, Dec 11, 2008 at 04:03:07PM -0800, Stephen Hemminger wrote: > On Thu, 11 Dec 2008 13:15:28 -0500 > Neil Horman <nhorman@...driver.com> wrote: > > > On Thu, Dec 11, 2008 at 09:01:04AM -0800, Stephen Hemminger wrote: > > > 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. > > > > > > > There was previously good cause to use __netif_rx_complete instead of > > netif_rx_complete some time ago when multiqueue rx was implemented using a set > > of dummy netdevices. But with the separation of the napi code, there is no > > longer any reason for this to be done. > > > > I just took a quick look, and it appears that sky2 is the last remaining driver > > to use the underlying napi routines. > > > > This patch maintains exactly the same functionality that it previously had, but > > allows for the netpoll patch to be safe with respect to the per-cpu poll_lists > > used by net_rx_action. > > > > Regards > > Neil > > > > > > Signed-off-by: Neil Horman <nhorman@...driver.com> > > > > > > sky2.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/drivers/net/sky2.c b/drivers/net/sky2.c > > index 3813d15..84bdc3c 100644 > > --- a/drivers/net/sky2.c > > +++ b/drivers/net/sky2.c > > @@ -2694,7 +2694,7 @@ static int sky2_poll(struct napi_struct *napi, int work_limit) > > sky2_write8(hw, STAT_TX_TIMER_CTRL, TIM_STOP); > > sky2_write8(hw, STAT_TX_TIMER_CTRL, TIM_START); > > } > > - napi_complete(napi); > > + netif_rx_complete(napi->dev, napi); > > sky2_read32(hw, B0_Y2_SP_LISR); > > done: > > I would ask it the other way. Why is interface an argument to netif_rx_complete > if it is never used? > Thats a fair question, and I don't know the answer, Dave? Neil -- /**************************************************** * Neil Horman <nhorman@...driver.com> * Software Engineer, Red Hat ****************************************************/ -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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