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

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Message-Id: <200701311713.04104.oliver@neukum.org>
Date:	Wed, 31 Jan 2007 17:12:51 +0100 (MET)
From:	Oliver Neukum <oliver@...kum.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Pavel Machek <pavel@....cz>, "Rafael J. Wysocki" <rjw@...k.pl>,
	pm list <linux-pm@...ts.osdl.org>, linux-kernel@...r.kernel.org
Subject: Re: [linux-pm] question on resume()

Am Mittwoch, 31. Januar 2007 16:54 schrieb Alan Stern:
> On Wed, 31 Jan 2007, Pavel Machek wrote:

> > "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.
> 
> There may be I/O requests sitting in a queue, already submitted by
> userspace.  The suspend method should wait for existing I/O to complete
> and stop processing new entries from the queue.

As far as I understand it now, a frozen process will be in the refrigerator.
Thus it cannot be blocking somewhere else in kernel space. Yet we cannot
be sure there's no queued IO, as theres aio.


> > > 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.
> 
> Again you misunderstood the question.  The driver must start queued I/O
> when its resume() method is called.  It should then be okay for the driver
> to call wake_up_interruptible(), even before tasks are unfrozen.

Isn't there some code in usbfs that'll do homegrown aio and deliver a
signal to a process if io is completed?

	Regards
		Oliver
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