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Date: Wed, 14 Mar 2007 15:23:10 -0400 (EDT)
From: Alan Stern <stern@rowland.harvard.edu>
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To: Cornelia Huck <cornelia.huck@de.ibm.com>
cc: Linus Torvalds <torvalds@linux-foundation.org>,
       Hugh Dickins <hugh@veritas.com>,
       Dmitry Torokhov <dmitry.torokhov@gmail.com>,
       Oliver Neukum <oneukum@suse.de>, Maneesh Soni <maneesh@in.ibm.com>,
       <gregkh@suse.de>, Richard Purdie <rpurdie@rpsys.net>,
       James Bottomley <James.Bottomley@SteelEye.com>,
       Kernel development list <linux-kernel@vger.kernel.org>
Subject: Re: 2.6.21-rc suspend regression: sysfs deadlock
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On Wed, 14 Mar 2007, Cornelia Huck wrote:

> On Wed, 14 Mar 2007 12:12:37 -0400 (EDT),
> Alan Stern <stern@rowland.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