linux-kernel - Re: Towards eliminating the freezer

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Date:	Tue, 24 Jul 2007 18:14:11 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Oliver Neukum <oliver@...kum.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-pm <linux-pm@...ts.linux-foundation.org>
Subject: Re: Towards eliminating the freezer

On Tue, 24 Jul 2007, Rafael J. Wysocki wrote:

> > Then device_suspend() can be simplified:
> > 
> > int device_suspend(pm_message_t state)
> > {
> > 	int error = 0;
> > 
> > 	might_sleep();
> > 	list_for_each_entry_reverse(dev, &dpm_locked, power.entry) {
> > 		error = suspend_device(dev, state);
> > 
> > 		if (error) {
> > 			printk(KERN_ERR "Could not suspend device %s: "
> > 				"error %d%s\n",
> > 				kobject_name(&dev->kobj), error,
> > 				error == -EAGAIN ? " (please convert to suspend_late)" : "");
> > 			break;
> > 		}
> > 		list_move(&dev->power.entry, &dpm_off);
> 
> Is that safe with list_for_each_entry_reverse?

No.  I guess it'll have to resemble the other code.

> Yes, that looks fine. 
> 
> So, who's writing the patch? ;-)

I can do it.  You haven't made any changes to this part of the code, 
have you?  My work tends to be based on Linus's tree, not -mm.

Something to watch out for: With all the extra locking, we run the risk
of blocking the keventd workqueue.  This may or may not matter, but to
be safe perhaps there should be a new general-purpose workqueue which
_expects_ to block (or freeze) during suspends.  Any work routine that 
involves adding or removing a device should go on the new workqueue.

> > Incidentally, what is dpm_mtx for?  It doesn't seem to do anything 
> > useful.  Is it a relic of the former runtime PM support?
> 
> I think so.  IMO it can be removed.
> 
> I also think it would be nicer to have all of the functions in
> drivers/base/power/{main|suspend|resume}.c moved to one file.

Yes, they are all similar enough that there isn't much point keeping 
them separate.

Alan Stern

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