linux-kernel - Re: [PATCH net] net: hyperv: initialize link status correctly

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Message-ID: <1390818638.2735.136.camel@deadeye.wl.decadent.org.uk>
Date:	Mon, 27 Jan 2014 10:30:38 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Jason Wang <jasowang@...hat.com>
Cc:	David Miller <davem@...emloft.net>, kys@...rosoft.com,
	haiyangz@...rosoft.com, devel@...uxdriverproject.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: hyperv: initialize link status correctly

On Mon, 2014-01-27 at 18:28 +0800, Jason Wang wrote:
> On 01/27/2014 06:22 PM, Ben Hutchings wrote:
> > On Mon, 2014-01-27 at 17:40 +0800, Jason Wang wrote:
> >> On 01/27/2014 04:35 PM, David Miller wrote:
> >>> From: Jason Wang <jasowang@...hat.com>
> >>> Date: Mon, 27 Jan 2014 15:30:54 +0800
> >>>
> >>>> Call netif_carrier_on() after register_device(). Otherwise it won't work since
> >>>> the device was still in NETREG_UNINITIALIZED state.
> >>>>
> >>>> Fixes a68f9614614749727286f675d15f1e09d13cb54a
> >>>> (hyperv: Fix race between probe and open calls)
> >>>>
> >>>> Cc: Haiyang Zhang <haiyangz@...rosoft.com>
> >>>> Cc: K. Y. Srinivasan <kys@...rosoft.com>
> >>>> Reported-by: Di Nie <dnie@...hat.com>
> >>>> Tested-by: Di Nie <dnie@...hat.com>
> >>>> Signed-off-by: Jason Wang <jasowang@...hat.com>
> >>> A device up can occur at the moment you call register_netdevice(),
> >>> therefore that up call can see the carrier as down and fail or
> >>> similar.  So you really cannot resolve the carrier to be on in this
> >>> way.
> >> True, we need a workqueue to synchronize them.
> > Whatever for?  All you need to do is:
> >
> > 	rtnl_lock();
> > 	register_netdevice();
> > 	netif_carrier_on();
> > 	rtnl_unlock();
> >
> > It would be nice if we could make the current code work with a change in
> > the core, though.
> >
> > Ben.
> >
> 
> Looks like the link status interrupt may happen during this (after
> netvsc_device_add() was called by rndis_filter_device_add()) without any
> synchronization. This may lead a wrong link status here.

Now I'm confused - if there's a link status interrupt, why are you
setting the carrier on initially?

Ben.

-- 
Ben Hutchings
If at first you don't succeed, you're doing about average.

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