linux-kernel - Re: loading firmware while usermodehelper disabled.

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Date:	Sun, 1 Jan 2012 11:17:52 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Oliver Neukum <oliver@...kum.org>
cc:	Matthew Garrett <mjg@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Larry Finger <Larry.Finger@...inger.net>,
	Chaoming Li <chaoming_li@...lsil.com.cn>,
	"John W. Linville" <linville@...driver.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	USB list <linux-usb@...r.kernel.org>,
	Linux Wireless List <linux-wireless@...r.kernel.org>
Subject: Re: loading firmware while usermodehelper disabled.

On Sun, 1 Jan 2012, Oliver Neukum wrote:

> Am Sonntag, 1. Januar 2012, 03:21:45 schrieb Alan Stern:
> > On Sat, 31 Dec 2011, Oliver Neukum wrote:
> 
> > > We are definitely going through do_unbind_rebind(). But I don't think
> > > it matters why we got there. We seem to be calling probe() too early.
> > > And we need to guarantee that a driver can request firmware in probe()
> > > 
> > > So something has changed in the resume code path further up.
> > 
> > For at least a year and a half, it has been true that rebinding takes
> 
> Yes, so I don't understand why we haven't been hitting this issue
> all that time.

Perhaps if Matthew compared logs from an old and a new system with 
appropriate debugging options configured, something might show up.

> > place during the complete phase of system resume.  Clearly that is too 
> > early to load firmware.  When do you think we should do it instead?
> 
> I think we ought to delay until right after user space is unfrozen.
> The devices are gone anyway, so we lose nothing but have the ability
> to call helpers.

That's true.  But doing it will be a nuisance.  The nice thing about 
the current situation is that the driver core automatically iterates 
over all interfaces.

> > And how should we keep track of which interfaces need rebinding?
> 
> I guess this calls for a brute force approach. We can kick khubd and have
> it walk all busses checking for  needs_binding.

Ugh.  At a minimum, let's use a different process, not khubd.

As Linus pointed out, the real problem here is the firmware loader.  
The way it is now, a driver can't always depend on the data being
available, even during a normal boot.  It ought to use an asynchronous
approach; then none of these problems would arise.

Alan Stern

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