linux-kernel - Re: [linux-pm] Is it supposed to be ok to call del

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Message-ID: <Pine.LNX.4.44L0.1003011021440.1645-100000@iolanthe.rowland.org>
Date:	Mon, 1 Mar 2010 10:23:27 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Pavel Machek <pavel@....cz>
cc:	Jens Axboe <jens.axboe@...cle.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Maxim Levitsky <maximlevitsky@...il.com>,
	linux-pm <linux-pm@...ts.linux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [linux-pm] Is it supposed to be ok to call del_gendisk while
 userspace is frozen?

On Mon, 1 Mar 2010, Pavel Machek wrote:

> Hi!
> 
> > > > This is a matter for Jens.  Is the bdi writeback task freezable?  If it
> > > > is, should it be made unfreezable?
> > > 
> > > I'm not a big expect on what tasks should be freezable or not. As it
> > > stands, the writeback tasks will attempt to freeze and thaw with the
> > > system. I guess that screws the sync from resume call, since it's not
> > > running and the sync will wait for it to retrieve and finish that work
> > > item.
> > > 
> > > To the suspend experts - can we safely mark the writeback tasks as
> > > non-freezable?
> > 
> > The reason for freezing those tasks is to avoid writebacks at random
> > times during a system sleep transition, when the underlying device may
> > already be suspended, right?
> 
> It is also there to avoid inconsistency between in-filesystem data and
> snapshot in hibernation image.

A good point, although in this case I think it won't matter.  Writing
out a dirty page twice (once right after taking the snapshot and then
again after resuming from hibernation) will leave the disk in a correct
state.

Alan Stern

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