Messages in this thread | | | Date | Wed, 15 Jan 2014 11:47:02 +0000 | From | Zoltan Kiss <> | Subject | Re: [PATCH net-next] xen-netback: Rework rx_work_todo |
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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
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