linux-kernel - Re: [RFC][PATCH] PM: Introduce new top level suspend and hibernation callbacks (rev. 3)

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Date:	Wed, 26 Mar 2008 10:03:38 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	pm list <linux-pm@...ts.linux-foundation.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Greg KH <greg@...ah.com>, Len Brown <lenb@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Alexey Starikovskiy <astarikovskiy@...e.de>,
	David Brownell <david-b@...bell.net>,
	Pavel Machek <pavel@....cz>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [RFC][PATCH] PM: Introduce new top level suspend and hibernation
 callbacks (rev. 3)

On Tue, 25 Mar 2008, Rafael J. Wysocki wrote:

> > I just thought of another problem.  At the point where
> > local_irq_disable() is called, in between device_suspend() and
> > device_power_down(), it is possible in a preemptible kernel that
> > another task is holding dpm_list_mtx and is in the middle of updating
> > the list pointers.  This would mess up the traversal in
> > device_power_down().
> > 
> > I'm not sure about the best way to prevent this.  Is it legal to call
> > unlock_mutex() while interrupts or preemption are disabled?
> 
> Well, I think it is, but I'm not sure how that can help.
> 
> To prevent the race from happening, we can lock dpm_list_mtx before switching
> interrupts off in kernel/power/main.c:suspend_enter() and analogously in
> kernel/power/disk.c .

That's right.  And once interrupts are turned off you should unlock 
dpm_list_mtx again, in case a noirq method wants to unregister a 
device.  Hence my question: Is it legal to call unlock_mutex() while 
interrupts are disabled?

Alan Stern

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