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

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Message-ID: <Pine.LNX.4.44L0.0801052249060.8784-100000@netrider.rowland.org>
Date:	Sat, 5 Jan 2008 23:04:33 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
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 Sat, 5 Jan 2008, Rafael J. Wysocki wrote:

> On Saturday, 5 of January 2008, Alan Stern wrote:
> > On Sat, 5 Jan 2008, Rafael J. Wysocki wrote:

> > > Still, even doing that is not enough, since someone can call
> > > destroy_suspended_device() from a .suspend() routine and then the device
> > > will end up on a wrong list just as well.
> > 
> > That should never happen.  The whole idea of destroy_suspended_device()
> > is that the device couldn't be resumed and in fact should be
> > unregistered because it is no longer working or no longer present.  A
> > suspend routine won't detect this sort of thing since it doesn't try to
> > resume the device.
> > 
> > But it wouldn't hurt to mention in the kerneldoc that 
> > destroy_suspended_device() is meant to be called only during a system 
> > resume.
> 
> Hmm.  Please have a look at the appended patch.
> 
> I have removed the warning from device_del() and used list_empty() to detect
> removed devices in the .suspend() routines.  Is that viable?

It's not good.

The warning in device_del() is vital.  It's what will tell people where
the problem is when a deadlock occurs during system resume because some
driver has mistakenly tried to unregister a device at the wrong time.  
It would have pointed immediately to the msr driver in the case of the
bug Andrew found, for instance.

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(), I suppose that would be okay.

Alan Stern



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