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

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Message-Id: <200801061419.52277.rjw@sisk.pl>
Date:	Sun, 6 Jan 2008 14:19:51 +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, Alan Stern wrote:
> 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(),

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))

> I suppose that would be okay. 

Rafael
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