netdev - RE: [PATCH net] xen-netback: fix vif tx queue race in xenvif_rx

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Message-ID: <9AAE0902D5BC7E449B7C8E4E778ABCD0200D0D@AMSPEX01CL01.citrite.net>
Date:	Thu, 9 Jan 2014 09:35:49 +0000
From:	Paul Durrant <Paul.Durrant@...rix.com>
To:	David Miller <davem@...emloft.net>,
	"majieyue@...il.com" <majieyue@...il.com>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	"jieyue.majy@...baba-inc.com" <jieyue.majy@...baba-inc.com>,
	"yingbin.wangyb@...baba-inc.com" <yingbin.wangyb@...baba-inc.com>,
	"tienan.ftn@...baba-inc.com" <tienan.ftn@...baba-inc.com>,
	Wei Liu <wei.liu2@...rix.com>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	David Vrabel <david.vrabel@...rix.com>
Subject: RE: [PATCH net] xen-netback: fix vif tx queue race in
 xenvif_rx_interrupt

> -----Original Message-----
> From: netdev-owner@...r.kernel.org [mailto:netdev-
> owner@...r.kernel.org] On Behalf Of David Miller
> Sent: 08 January 2014 20:12
> To: majieyue@...il.com
> Cc: netdev@...r.kernel.org; xen-devel@...ts.xen.org; jieyue.majy@...baba-
> inc.com; yingbin.wangyb@...baba-inc.com; tienan.ftn@...baba-inc.com; Wei
> Liu; Ian Campbell; David Vrabel
> Subject: Re: [PATCH net] xen-netback: fix vif tx queue race in
> xenvif_rx_interrupt
> 
> From: Ma JieYue <majieyue@...il.com>
> Date: Thu,  9 Jan 2014 03:24:21 +0800
> 
> > -	if (xenvif_rx_schedulable(vif))
> > +	if (netif_queue_stopped(vif->dev) && xenvif_rx_schedulable(vif))
> 
> I do not see anything which prevents a netif_stop_queue() call from
> happening
> between these two tests in another thread of control.
> 
> This therefore looks like a bandaid and not a real fix.

My fix "xen-netback: improve guest-receive-side flow control" in net-next will make this change irrelevant as it completely removes all this somewhat fragile code.

  Paul

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