linux-kernel - Re: [PATCH] firmware loader: don't cancel _nowait requests when helper is not yet available

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Date:	Fri, 16 Mar 2012 22:14:42 +0100
From:	Christian Lamparter <chunkeey@...glemail.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Kay Sievers <kay@...y.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, alan@...rguk.ukuu.org.uk,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux PM mailing list <linux-pm@...r.kernel.org>,
	skannan@...eaurora.org, Stephen Boyd <sboyd@...eaurora.org>
Subject: Re: [PATCH] firmware loader: don't cancel _nowait requests when helper is not yet available

> That's fine by me.
> 
> If no one objects, I'll apply it.

Congrats on that nice, long and "obvious" explanation. Really,
what do you mean by the "end of resume"? As far as I know it
is NOT "after" all ->resume calls have finished, in fact the
usermodehelper is still disabled during ->complete! Maybe a
hint about "after/before function X() has finished/starts" 

Furthermore, I wonder what happends about built-in modules
for devices that need a firmware at probe [e.g.: different
firmware support different special features. This is quite
common for wifi stuff. e.g.: Special firmwares for APs]?

Because As far as I know "driver_init();" is called before
"usermodehelper_enable();" in "do_basic_setup()".
So, theoretical these people should see the same WARNINGs
and read the comment about suspend/resume and I'm sure
they will be thinking: WTF! 

Regards,
	Chr
> > ---
> > 
> >  drivers/base/firmware_class.c |   16 ++++++++++++++++
> >  1 files changed, 16 insertions(+), 0 deletions(-)
> > 
> > diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
> > index 6c9387d..9199e3e 100644
> > --- a/drivers/base/firmware_class.c
> > +++ b/drivers/base/firmware_class.c
> > @@ -535,6 +535,22 @@ static int _request_firmware(const struct firmware **firmware_p,
> >  
> >  	read_lock_usermodehelper();
> >  
> > +	/*
> > +	 * It is wrong to request firmware when the system is suspended,
> > +	 * because it simply won't work. Also, it can cause races with
> > +	 * the freezer, leading to freezing failures. Worse than that,
> > +	 * it may even cause a user space process to run when we think
> > +	 * we have frozen the user space! - and that can lead to all kinds
> > +	 * of interesting breakage..
> > +	 *
> > +	 * So check if the system is in a state which is unsuitable for
> > +	 * requesting firmware (because it is suspended or not yet fully
> > +	 * resumed) and bail out early if needed.
> > +	 * Usermodehelpers are disabled at the beginning of suspend, before
> > +	 * freezing tasks and re-enabled only towards the end of resume, after
> > +	 * thawing tasks, when it is safe. So all we need to do here is ensure
> > +	 * that we don't request firmware when usermodehelpers are disabled.
> > +	 */
> >  	if (WARN_ON(usermodehelper_is_disabled())) {
> >  		dev_err(device, "firmware: %s will not be loaded\n", name);
> >  		retval = -EBUSY;
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