linux-kernel - Re: Problem with freezable workqueues

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Message-ID: <20070228193234.GA86@tv-sign.ru>
Date:	Wed, 28 Feb 2007 22:32:34 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	vatsa@...ibm.com, Pavel Machek <pavel@....cz>,
	Gautham R Shenoy <ego@...ibm.com>,
	Johannes Berg <johannes@...solutions.net>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Problem with freezable workqueues

On 02/28, Rafael J. Wysocki wrote:
>
> > --- workqueue.c.org	2007-02-28 18:32:48.000000000 +0530
> > +++ workqueue.c	2007-02-28 18:44:23.000000000 +0530
> > @@ -718,6 +718,8 @@ static void cleanup_workqueue_thread(str
> >  		insert_wq_barrier(cwq, &barr, 1);
> >  		cwq->should_stop = 1;
> >  		alive = 1;
> > +		if (frozen(cwq->thread))
> > +			thaw(cwq->thread);
> >  	}
> >  	spin_unlock_irq(&cwq->lock);
>
> Unfortunately, the above code is mm-only.  Is the analogous fix for 2.6.21-rc2
> viable?

I am sorry, I lost track of this problem. As for 2.6.21, create_freezeable_workqueue
doesn't work and conflict with suspend. Why can't we remove it from XFS as you
suggested before?

Iirc,
	On 02/28, Nigel Cunningham wrote:
	>
	> On Wed, 2007-02-28 at 01:08 +0100, Rafael J. Wysocki wrote:
	> > On Wednesday, 28 February 2007 01:01, Johannes Berg wrote:
	> > > On Wed, 2007-02-28 at 00:57 +0100, Rafael J. Wysocki wrote:
	> > >
	> > > > Okay, in that case I'd suggest removing create_freezeable_workqueue() and
	> > > > make all workqueues nonfreezable once again for 2.6.21 (as far as I know, only
	> > > > the two XFS workqueues are affected).
	> > >
	> > > I think Nigel might object but I forgot what specific trouble XFS was
	> > > causing him.
	> >
	> > We suspected that the XFS' worker threads might commit I/O after
	> > freeze_processes() has returned, but that hasn't been supported by evidence,
	> > as far as I can recall.
	> >
	> > Also, making them freezable was controversial ...
	>
	> Controversy is no reason to give in! Nevertheless, I think you're right
	> - I believe the XFS guys said they fixed the issue that had caused I/O
	> to be submitted post-freeze. Well, we'll see if it appears again, won't
	> we?

Oleg.

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