linux-kernel - Re: 2.6.21-rc suspend regression: sysfs deadlock

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Message-ID: <20070315112725.7eadb7b7@gondolin.boeblingen.de.ibm.com>
Date:	Thu, 15 Mar 2007 11:27:25 +0100
From:	Cornelia Huck <cornelia.huck@...ibm.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Hugh Dickins <hugh@...itas.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Oliver Neukum <oneukum@...e.de>,
	Maneesh Soni <maneesh@...ibm.com>, <gregkh@...e.de>,
	Richard Purdie <rpurdie@...ys.net>,
	James Bottomley <James.Bottomley@...elEye.com>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.21-rc suspend regression: sysfs deadlock

On Wed, 14 Mar 2007 15:23:10 -0400 (EDT),
Alan Stern <stern@...land.harvard.edu> wrote:

> > > +struct other_task_struct {
> > > +	struct kobject 		*kobj;
> > > +	void			(*func)(void *);
> > > +	void			*data;
> > > +	struct work_struct	work;
> > > +};
> > > +
> > > +static void other_task_work(struct work_struct *work)
> > > +{
> > > +	struct other_task_struct *ots = container_of(work,
> > > +			struct other_task_struct, work);
> > > +
> > > +	(ots->func)(ots->data);
> > > +	kobject_put(ots->kobj);
> > > +	kfree(ots);
> > > +}
> > 
> > The naming seems a bit unintuitive, but I don't have a good
> > alternative idea. Perhaps sysfs_work_struct, sysfs_delayed_work()?
> 
> sysfs_work_struct is too generic; other parts of sysfs might also want to
> use workqueues for different purposes.

> I don't like calling it "delayed"-anything, because the operations aren't
> necessarily delayed!  On an SMP system they might even execute before the
> sysfs_access_in_other_task() call returns.  (Although the two examples we
> have so far can't do that because of lock contention.)

Sure. But then you shouldn't refer to "delay" in the comments for the
functions as well :)

> The major feature added here is that the work takes place in a different 
> task's context, not that it is delayed.  Hence the choice of names.

Hm. Perhaps device_schedule_access()?
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