linux-kernel - Re: [PATCH] PM: Acquire device locks on suspend

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Date:	Sat, 5 Jan 2008 21:19:47 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Greg KH <gregkh@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Len Brown <lenb@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>
Subject: Re: [PATCH] PM: Acquire device locks on suspend

On Saturday, 5 of January 2008, Alan Stern wrote:
> On Sat, 5 Jan 2008, Rafael J. Wysocki wrote:
> 
> > Greg, Andrew,
> > 
> > The appended patch is a replacement for
> > gregkh-driver-pm-acquire-device-locks-prior-to-suspending.patch that deadlocked
> > suspend and hibernation on some systems.
> > 
> > Please consider for applying.
> 
> This warning message:
> 
> > @@ -905,6 +915,13 @@ void device_del(struct device * dev)
> >  	struct device * parent = dev->parent;
> >  	struct class_interface *class_intf;
> >  
> > +	if (pm_sleep_lock()) {
> > +		dev_warn(dev, "Illegal %s during suspend\n", __FUNCTION__);
> > +		dump_stack();
> > +	} else {
> 
> will unavoidably be triggered by this code:

Ah, my fault, sorry.

> > +void device_pm_destroy_suspended(struct device *dev)
> > +{
> > +	pr_debug("PM: Removing suspended device %s:%s\n",
> > +		 dev->bus ? dev->bus->name : "No Bus",
> > +		 kobject_name(&dev->kobj));
> > +	mutex_lock(&dpm_list_mtx);
> > +	list_del_init(&dev->power.entry);
> > +	mutex_unlock(&dpm_list_mtx);
> > +	up(&dev->sem);
> > +	device_unregister(dev);
> > +}
> 
> since the call to device_del() will occur while the pm_sleep_rwsem is
> still locked for writing.  That's why I suggested not unregistering
> these devices until after everything else has been resumed and the
> rwsem has been dropped.

Hmm, well.  I'll go back to the previous version, then.  Sorry for the mess.

> Another thing to watch out for: Just in case somebody ends up calling
> destroy_suspended_device(dev) from within dev's own resume method, you 
> should interchange the resume_device() and the list_move_tail() 
> calls in dpm_resume().

However, if we unregister them all at once after releasing pm_sleep_rwsem,
that shouldn't be necessary, right?

Rafael
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