netdev - Re: [PATCH net-next] xen-netback: Rework rx_work

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Message-ID: <20140115103707.GI5698@zion.uk.xensource.com>
Date:	Wed, 15 Jan 2014 10:37:07 +0000
From:	Wei Liu <wei.liu2@...rix.com>
To:	Zoltan Kiss <zoltan.kiss@...rix.com>
CC:	<ian.campbell@...rix.com>, <wei.liu2@...rix.com>,
	<xen-devel@...ts.xenproject.org>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <jonathan.davies@...rix.com>
Subject: Re: [PATCH net-next] xen-netback: Rework rx_work_todo

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?

> 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?

Wei.

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