From mboxrd@z Thu Jan 1 00:00:00 1970 From: Zoltan Kiss Subject: Re: [PATCH net-next] xen-netback: Rework rx_work_todo Date: Wed, 15 Jan 2014 11:47:02 +0000 Message-ID: <52D67536.4030106@citrix.com> References: <1389727719-21439-1-git-send-email-zoltan.kiss@citrix.com> <20140115103707.GI5698@zion.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Cc: , , , , To: Wei Liu Return-path: In-Reply-To: <20140115103707.GI5698@zion.uk.xensource.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 15/01/14 10:37, Wei Liu wrote: > On Tue, Jan 14, 2014 at 07:28:39PM +0000, Zoltan Kiss wrote: >> The recent patch to fix receive side flow control (11b57f) solved the spinning >> thread problem, however caused an another one. The receive side can stall, if: >> - xenvif_rx_action sets rx_queue_stopped to false >> - interrupt happens, and sets rx_event to true >> - then xenvif_kthread sets rx_event to false >> > > If you mean "rx_work_todo" returns false. > > In this case > > (!skb_queue_empty(&vif->rx_queue) && !vif->rx_queue_stopped) || vif->rx_event; > > can still be true, can't it? Sorry, I should wrote rx_queue_stopped to true > >> Also, through rx_event a malicious guest can force the RX thread to spin. This >> patch ditch that two variable, and rework rx_work_todo. If the thread finds it > > This seems to be a bigger problem. Can you elaborate? My mistake too. I forgot that rx_action set it to false, so it's not really a spinning. However the thread should still run xenvif_rx_action to figure out there is no space in the ring before it sets rx_event to false. In my patch we can quit earlier. Zoli