linux-kernel - Re: [linux-pm] Re: [PATCH] Remove process freezer from suspend to RAM pathway

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Message-Id: <200707032320.20334.rjw@sisk.pl>
Date:	Tue, 3 Jul 2007 23:20:19 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	stern@...land.harvard.edu, oliver@...kum.org, mjg59@...f.ucam.org,
	linux-kernel@...r.kernel.org, pavel@....cz,
	linux-pm@...ts.linux-foundation.org
Subject: Re: [linux-pm] Re: [PATCH] Remove process freezer from suspend to RAM pathway

On Tuesday, 3 July 2007 22:19, Miklos Szeredi wrote:
> > > Well, but you did remove sys_sync() from the freezer, which is
> > > and must be called in the hibernate path.
> > 
> > That's not really true.  We _want_ to call sys_sync() in both the 
> > hibernate and suspend paths (in case the batteries run down), to help 
> > avoid filesystem problems if something goes wrong with the resume.  But 
> > it isn't a hard requirement.
> > 
> > > > I'm not sure why this can't be made atomic, but assuming, that it
> > > > can't, fuse should still not need to be implicated.  If it is, that's
> > > > an indication about something wrong in the suspend procedure.
> > > 
> > > Nope, something's wrong in fuse. You must be able to deal with sync
> > > until every task is frozen.
> > 
> > That's ridiculous.  FUSE itself runs partially as a user task.  How can
> > you expect it to carry out a sync or anything else when it is frozen?
> > 
> > I suppose you could "deal" with it by having the kernel portion return
> > an error if the userspace part is frozen.  If the hibernate/suspend 
> > code bothered to check the return value, it would immediately abort 
> > the suspend.

Er, do_sync() doesn't return a result.

> I strongly believe, that we don't want to deal with it.  If we want to
> call sync(), do it while the system is fully operational.  It's a best
> effort thing anyway, and you can loose data in other ways if resume
> fails.

The requirement of syncing when the system (including the user space) is fully
operational is FUSE-specific.  Thus we'd rather like to sync FUSE filesystems
before freezing the user space and freeze the other filesystems after freezing
the user space.

Greetings,
Rafael


-- 
"Premature optimization is the root of all evil." - Donald Knuth
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