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

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Message-Id: <201203150004.17076.rjw@sisk.pl>
Date:	Thu, 15 Mar 2012 00:04:16 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Saravana Kannan <skannan@...eaurora.org>,
	Kay Sievers <kay.sievers@...y.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	Christian Lamparter <chunkeey@...glemail.com>,
	linux-kernel@...r.kernel.org,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	alan@...rguk.ukuu.org.uk,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux PM mailing list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] firmware loader: don't cancel _nowait requests when helper is not yet available

On Wednesday, March 14, 2012, Stephen Boyd wrote:
> On 03/13/12 13:14, Rafael J. Wysocki wrote:
> > All of those use cases are in fact of the "wait for user space to be thawed
> > and then load the firmware" type, which I believe may be handled without
> > changing that code.
> >
> > Why don't you make your kthread freezable, for one example?
> >
> > Why don't you use a freezable workqueue instead?
> >
> 
> If we put it on the freezable workqueue or make it a freezable thread
> will it work?

That depends on what exactly you want to achieve, which isn't entirely clear
to me at this point.

> In my scenario a wakeup interrupt comes in that wakes us up from
> suspend. Within that wakeup handler a work item is scheduled to the
> freezable workqueue. That work item then calls request_firmware().

That should work.

> It looks like we call schedule() after thawing the workqueues and tasks
> so the work item could run before usermodehelpers are enabled and then
> request_firmware() would fail. Do we need something like this (ignore
> the fact that we call usermodhelper_enable() twice)?
> 
> diff --git a/kernel/power/process.c b/kernel/power/process.c
> index 7e42645..61bfa95 100644
> --- a/kernel/power/process.c
> +++ b/kernel/power/process.c
> @@ -187,6 +187,7 @@ void thaw_processes(void)
>         } while_each_thread(g, p);
>         read_unlock(&tasklist_lock);
>  
> +       usermodehelper_enable();

That would be a reasonable change.

>         schedule();
>         printk("done.\n");
>  }
> 
> 
> Is there a reason we disable usermodehelpers if
> CONFIG_SUSPEND_FREEZER=n?

Not really, but CONFIG_SUSPEND_FREEZER=n can only work reliably in a
very limited set of cases, so I don't think it's even worth making the
general code depend on it.

I'd actually prefer to remove CONFIG_SUSPEND_FREEZER altogether,
because it's not very useful nowadays (probably isn't useful at all).

> Should we do this instead so that
> usermodehelpers are only disabled if we freeze userspace? Also what is
> that schedule() call in thaw_kernel_threads() for? It looks like we'll
> call schedule between kernel thread thawing and userspace thawing.

Which is OK, I think.

> I pushed out the schedule() call to the callers so that we don't call
> schedule() until userspace is thawed.

Why did you do that?

Rafael
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