From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Re: [PATCH 6/7] [NETDEV]: tehuti Fix possible causing oops of net_rx_action Date: Wed, 12 Dec 2007 08:36:48 -0800 Message-ID: <20071212083648.13ab0aea@freepuppy.rosehill> References: <002901c83c73$b089b6e0$9c94fea9@jason> <20071211213939.122de1db@freepuppy.rosehill> <20071212.072034.148833113.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, jgarzik@pobox.com, baum@tehutinetworks.net, andy@greyhouse.net To: David Miller , joonwpark81@gmail.com Return-path: In-Reply-To: <20071212.072034.148833113.davem@davemloft.net> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Wed, 12 Dec 2007 07:20:34 -0800 (PST) David Miller wrote: > From: Stephen Hemminger > Date: Tue, 11 Dec 2007 21:39:39 -0800 > > > On Wed, 12 Dec 2007 13:01:27 +0900 > > "Joonwoo Park" wrote: > > > > > [NETDEV]: tehuti Fix possible causing oops of net_rx_action > > > > > > Signed-off-by: Joonwoo Park > > > --- > > > drivers/net/tehuti.c | 2 ++ > > > 1 files changed, 2 insertions(+), 0 deletions(-) > > > > > > diff --git a/drivers/net/tehuti.c b/drivers/net/tehuti.c > > > index 21230c9..955e749 100644 > > > --- a/drivers/net/tehuti.c > > > +++ b/drivers/net/tehuti.c > > > @@ -305,6 +305,8 @@ static int bdx_poll(struct napi_struct *napi, int budget) > > > > > > netif_rx_complete(dev, napi); > > > bdx_enable_interrupts(priv); > > > + if (unlikely(work_done == napi->weight)) > > > + return work_done - 1; > > > } > > > return work_done; > > > } > > > > A better fix would be not going over budget in the first place. > > That's not the problem. > > They are not going over the budget, rather, they are hitting > the budget yet doing netif_rx_complete() as well which is > illegal. > > Unless you strictly process less than "weight" packets, you must > not netif_rx_complete() and re-enable chip interrupts. > > I can't believe people are trying to fix this bug like this. Sorry, I was looking at a different possible problem. The issue is that if netdev_budget was set smaller (say 128) but device weight was set larger (say 256). The new code would still allow the device to do a full swipe (256) packets rather than only 128 as in earlier NAPI. I guess it is an okay behaviour change, because we don't really guarantee that case. The problem with the tehuti driver is the logic around priv->napi_stop. That whole early stop concept should be removed since it just duplicates the logic of netdev->weight but breaks the assumptions in the calling netif_rx_action. -- Stephen Hemminger