linux-kernel - Re: [linux-pm] wacom + runtime PM = AA deadlock

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Message-ID: <Pine.LNX.4.44L0.1009131600230.1315-100000@iolanthe.rowland.org>
Date:	Mon, 13 Sep 2010 16:02:16 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Oliver Neukum <oliver@...kum.org>
cc:	Jiri Slaby <jslaby@...e.cz>, Dmitry Torokhov <dtor@...l.ru>,
	<pingc@...om.com>, linux-pm <linux-pm@...ts.linux-foundation.org>,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>,
	<linux-input@...r.kernel.org>
Subject: Re: [linux-pm] wacom + runtime PM = AA deadlock

On Mon, 13 Sep 2010, Oliver Neukum wrote:

> Am Montag, 13. September 2010, 17:17:54 schrieb Alan Stern:
> > On Mon, 13 Sep 2010, Oliver Neukum wrote:
> > 
> > > PM in this driver looks broken. Please try this.
> > > 
> > > In short you want to drop the PM reference and depend on remote
> > > wakeup and busy marking for this driver. Currently it gets a reference
> > > on every open() but never drops it.
> > > 
> > > For locking you depend on the PM core's internal lock. You simply
> > > make sure you have a PM reference during open() and close()
> > 
> > Is there any point in resuming the device during close() just in order
> > to kill the interrupt URB?  It seems counterproductive -- if the device 
> > had been suspended then there wouldn't be any interrupt URB to kill in 
> > the first place.
> 
> Suppose the device does not support remote wakeup. It would never
> be autosuspended while it is open, but simply resetting the flag
> would never reach the PM layer.

Whoops, that's right.  I didn't see the assignment to 
needs_remote_wakeup.

How come wacom_open doesn't check to see if wacom->open is already set?

Alan Stern

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