linux-kernel - Re: [linux-pm] Re: Hibernation considerations

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Message-Id: <200707231427.45672.rjw@sisk.pl>
Date:	Mon, 23 Jul 2007 14:27:44 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	nigel@...el.suspend2.net, stern@...land.harvard.edu,
	nigel@...pend2.net, jbms@....edu, miltonm@....com,
	ying.huang@...el.com, linux-kernel@...r.kernel.org, david@...g.hm,
	linux-pm@...ts.linux-foundation.org
Subject: Re: [linux-pm] Re: Hibernation considerations

On Monday, 23 July 2007 14:14, Miklos Szeredi wrote:
> > On Monday, 23 July 2007 12:24, Miklos Szeredi wrote:
> > > > > The only thing to do is what Rafael has been working on: unfreeze
> > > > > things, hope the tasks sort themselves out, and try again.
> > > > 
> > > > That's what I'm questioning. Is there a more reliable way and we've
> > > > just given up too quickly?
> > > 
> > > There obviously _are_ more reliable ways.  A trivial one seems to be
> > > to just not require user tasks to finish syscalls.
> > > 
> > > Yeah, stopping user processes outside the kernel is convenient, but
> > > there's no fundamental reason why it is the only place where those
> > > tasks can be stopped.
> > 
> > The reason is that we want them to "park" in safe places, ie. where there
> > are no locks held etc.  Thus, these safe places need to be chosen somehow
> > and since they are not marked throughout the code, we choose the obvious
> > one. :-)
> 
> Why shouldn't locks be held?
> 
> No locks which are required for suspend must be held, sure.  But
> otherwise holding locks doesn't matter at all.
> 
> And I'm not saying that is trivial to do, but it might not be too hard
> either.
> 
> Rafael, can you please tell, what happened to that patch, that did not
> wait for tasks in uninterruptible sleep to be frozen?
> 
> That seemed like a magnificent approach compared to anything that has
> been proposed since.

Well, the freezer have failed to freeze tasks for a couple of times in my
test setup and I've had a couple of hangs.

I have an idea how to improve it, but that still requires some pending freezer
patches to go first.

Greetings,
Rafael


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