linux-kernel - Re: [PATCH 2.6.19 5/5] fs: freeze

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Message-Id: <200611092218.58970.rjw@sisk.pl>
Date:	Thu, 9 Nov 2006 22:18:57 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
Cc:	Alasdair G Kergon <agk@...hat.com>,
	Eric Sandeen <sandeen@...hat.com>,
	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org,
	dm-devel@...hat.com, Srinivasa DS <srinivasa@...ibm.com>,
	Nigel Cunningham <nigel@...pend2.net>,
	David Chinner <dgc@....com>
Subject: Re: [PATCH 2.6.19 5/5] fs: freeze_bdev with semaphore not mutex

Hi,

On Thursday, 9 November 2006 22:17, Pavel Machek wrote:
> Hi!
> 
> > > > OTOH I have no idea _how_ we can tell xfs that the processes have been
> > > > frozen.  Should we introduce a global flag for that or something?
> > > 
> > > I guess XFS should just do all the writes from process context, and
> > > refuse any writing when its threads are frozen... I actually still
> > > believe it is doing the right thing, because you can't really write to
> > > disk from timer.
> > 
> > This is from a work queue, so in fact from a process context, but from
> > a process that is running with PF_NOFREEZE.
> 
> Why not simply &~ PF_NOFREEZE on that particular process? Filesystems
> are free to use threads/work queues/whatever, but refrigerator should
> mean "no writes to filesystem" for them...

But how we differentiate worker_threads used by filesystems from the
other ones?

BTW, I think that worker_threads run with PF_NOFREEZE for a reason,
but what exactly is it?

Rafael


-- 
You never change things by fighting the existing reality.
		R. Buckminster Fuller
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