netdev - RE: [PATCH 1/1] net/hyperv: Fix the code handling tx busy

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Date:	Mon, 19 Mar 2012 19:17:27 +0000
From:	Haiyang Zhang <haiyangz@...rosoft.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Stephen Hemminger <shemminger@...tta.com>,
	KY Srinivasan <kys@...rosoft.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>
Subject: RE: [PATCH 1/1] net/hyperv: Fix the code handling tx busy



> -----Original Message-----
> From: Eric Dumazet [mailto:eric.dumazet@...il.com]
> Sent: Monday, March 19, 2012 2:31 PM
> To: Haiyang Zhang
> Cc: Stephen Hemminger; KY Srinivasan; davem@...emloft.net;
> netdev@...r.kernel.org; linux-kernel@...r.kernel.org;
> devel@...uxdriverproject.org
> Subject: RE: [PATCH 1/1] net/hyperv: Fix the code handling tx busy
> 
> On Mon, 2012-03-19 at 17:50 +0000, Haiyang Zhang wrote:
> 
> > As in my previous reply to Eric --
> > We actually stop queue when the ring buffer is busy, see the code in
> > netvsc.c
> >
> > I have tested with one CPU. After NETDEV_TX_BUSY is returned, the
> > Linux guest OS continues to respond without any problem.
> 
> Then something is wrong somewhere.
> 
> Dont hide a bug adding a trick.
> 
> If you ever return NETDEV_TX_BUSY from start_xmit(), then you MUST call
> netif_tx_stop_queue() as well right before.

Yes, we called the stop_queue before returning NETDEV_TX_BUSY.

The stop_queue was called in the function netvsc_send() in file netvsc.c, then it returns to rndis_filter_send(), which returns to netvsc_start_xmit() in file netvsc_drv.c. So the NETDEV_TX_BUSY is indeed returned AFTER queue is stopped.

Thanks,
- Haiyang