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

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Date:	Sun, 6 Jan 2008 23:19:36 +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 Sunday, 6 of January 2008, Rafael J. Wysocki wrote:
> On Sunday, 6 of January 2008, Rafael J. Wysocki wrote:
> > On Sunday, 6 of January 2008, Alan Stern wrote:
> > > On Sun, 6 Jan 2008, Rafael J. Wysocki wrote:
> > > 
> > > > > If you can figure out a way to disable the warning in device_del() for 
> > > > > just the one device being unregistered by 
> > > > > device_pm_destroy_suspended(),
> > > > 
> > > > Something like this, perhaps:
> > > > 
> > > > @@ -905,6 +915,18 @@ void device_del(struct device * dev)
> > > >  	struct device * parent = dev->parent;
> > > >  	struct class_interface *class_intf;
> > > >  
> > > > +	if (down_trylock(&dev->sem)) {
> > > > +		if (pm_sleep_lock()) {
> > > > +			dev_warn(dev, "Illegal %s during suspend\n",
> > > > +				__FUNCTION__);
> > > > +			dump_stack();
> > > > +		} else {
> > > > +			pm_sleep_unlock();
> > > > +		}
> > > > +	} else {
> > > > +		up(&dev->sem);
> > > > +	}
> > > > +
> > > >  	if (parent)
> > > >  		klist_del(&dev->knode_parent);
> > > >  	if (MAJOR(dev->devt))
> > > 
> > > Bizarre, but it should work.
> > 
> > OK
> > 
> > Still, shouldn't we fail the removal of the device apart from giving the
> > warning?
> 
> Actually, having thought about it a bit more, I don't see the point in
> preventing the removal of the device from the list in device_pm_remove() if
> we allow all of the operations in device_del() preceding it to be performed.
> 
> Shouldn't we just take pm_sleep_rwsem in device_del() upfront and block on that
> if locked?

Ugh, the $subject patch looks like a city of races.  I'm struggling to close
them all, but it's getting complicated.

I'll post the result in a new thread.

Thanks,
Rafael
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