Re: [PATCH 0/5] Call netif_carrier_off() after register_netdev()

On Tue, 2012-08-14 at 14:00 -0700, David Miller wrote:

From: Ilya Shchepetkov <redacted>
Date: Tue, 14 Aug 2012 14:28:50 +0400

quoted

Hi,

There are several patches on the subject:
	
	31bde1ceaa873bcaecd49e829bfabceacc4c512d
	c55ad8e56b983f03589b38b4504b5d1f41161ff8
	e826eafa65c6f1f7c8db5a237556cebac57ebcc5
	0d672e9f8ac320c6d1ea9103db6df7f99ea20361
	6a3c869a6021f4abcd69aa5fbb15c63f69eb36fe

In 2008, David Miller wrote in his commit:
(b47300168e770b60ab96c8924854c3b0eb4260eb)

quoted

net: Do not fire linkwatch events until the device is registered.

quoted

Several device drivers try to do things like netif_carrier_off()
before register_netdev() is invoked.  This is bogus, but too many
drivers do this to fix them all up in one go.

But I don't understand what will happen in this case?

Sigh... I would strongly suggest that when you don't understand
something you leave it alone until you do.

You can't do the netif_carrier_off() after the device register because
at the precise moment the device is registered it can be openned in
parallel on another cpu and thus cause the entire carrier state
to be changed.

Therefore if you do the netif_carrier_off() afterwards, it might
be overwriting state changes made in another context.

Please just leave this code alone.

But if you do it beforehand then it doesn't have the intended effect.
(Supposed to be fixed by 22604c866889c4b2e12b73cbf1683bda1b72a313, which
had to be reverted: c276e098d3ee33059b4a1c747354226cec58487c.)

So you have to do it after, but without dropping the RTNL lock in
between.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.