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

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Message-ID: <Pine.LNX.4.44L0.0703141516150.7723-100000@iolanthe.rowland.org>
Date:	Wed, 14 Mar 2007 15:23:10 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Cornelia Huck <cornelia.huck@...ibm.com>
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, Cornelia Huck wrote:

> On Wed, 14 Mar 2007 12:12:37 -0400 (EDT),
> Alan Stern <stern@...land.harvard.edu> wrote:
> 
> > This seems more elegant (not yet tested).  Cornelia, does it look okay to 
> > you?
> 
> Works for me (grouping & ungrouping ctc) and looks sane. Some more
> comments below.

Thank you.

> > +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.)

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.

Alan Stern

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