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

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Message-ID: <A1F3067C9B68744AA19F6802BAB8FFDC0DCEA9DE@TK5EX14MBXC223.redmond.corp.microsoft.com>
Date:	Mon, 19 Mar 2012 20:50:42 +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 4:47 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 19:17 +0000, Haiyang Zhang wrote:
> 
> > 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.
> >
> 
> Thats should be in your changelog, so that next time, reviewers dont have to
> spend their time to check you did it right, especially when
> start_xmit() code is not self contained or at least in a single file.
> 
> Each time we see a NETDEV_TX_BUSY in a patch, this is a sign of a possible
> problem.
> 
> Your initial changelog was :
> 
> Instead of dropping the packet, we keep the skb buffer, and return
> NETDEV_TX_BUSY to let upper layer retry send. This will not cause endless
> loop, because the host is taking data away from ring buffer.
> 
> And this is the typical message that doesnt explain why its safe.

Thanks for your time, I will re-submit the patch with the explanation in the change
log.

Thanks,
- Haiyang