linux-kernel - Re: [linux-pm] question on resume()

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Message-ID: <20070131103045.GA19640@elf.ucw.cz>
Date:	Wed, 31 Jan 2007 11:30:45 +0100
From:	Pavel Machek <pavel@....cz>
To:	Oliver Neukum <oliver@...kum.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Alan Stern <stern@...land.harvard.edu>,
	Oliver Neukum <oliver@...kum.name>,
	pm list <linux-pm@...ts.osdl.org>, linux-kernel@...r.kernel.org
Subject: Re: [linux-pm] question on resume()

Hi!

> > > So, this means, on suspend():
> > > 
> > > 1. Don't worry about TASK_UNINTERRUPTIBLE
> > > 2. Do worry about TASK_INTERRUPTIBLE
> > > We have to cease IO and must not call wake_up_interruptible()
> > 
> > "cease IO"? No, I believe it is enough not to start new I/O. Userspace
> > is frozen at that point, it can't ask you to do I/O.
> >
> > > Isn't that a race until suspend() is called?
> > 
> > I do not think so.
> 
> What about URBs in flight which are waited for with TASK_INTERRUPTIBLE?

Same thing as if someone sent a signal to that process. (We are
talking about user processes here, right? Kernel threads have to take
care themselves).

> > > On resume():
> > > 
> > > 1. Don't worry about TASK_UNINTERRUPTIBLE
> > > 2. Do not restart IO that may call wake_up_interruptible()
> > > 
> > > When do we restart such IO?
> > 
> > We reuse signal handling code to do that for us. It is same situation
> > as when someone signals task doing I/O.
> 
> What happens to tasks in TASK_INTERRUPTIBLE which are frozen?
> Are they interrupted and frozen?

Interrupted with fake signal, then frozen, yes.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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