linux-kernel - Re: [RFC PATCH -rt 2/2] RCU priority boosting additions to rcutorture

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Date:	Wed, 31 Jan 2007 21:46:16 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Nigel Cunningham <nigel@...el.suspend2.net>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, tglx@...utronix.de,
	dipankar@...ibm.com, tytso@...ibm.com, dvhltc@...ibm.com,
	oleg@...sign.ru, twoerner.k@...il.com, josh@...edesktop.org,
	billh@...ppy.monkey.org, nielsen.esben@...glemail.com,
	corbet@....net
Subject: Re: [RFC PATCH -rt 2/2] RCU priority boosting additions to rcutorture

On Thu, Feb 01, 2007 at 01:42:42PM +1100, Nigel Cunningham wrote:
> Hi Paul.
> 
> On Wed, 2007-01-31 at 18:31 -0800, Paul E. McKenney wrote:
> > Good to hear from you, Nigel!
> 
> Thanks :)
> 
> > Should indeed be OK to freeze during suspend/hibernate.  Will my
> > schedule_timeout_interruptible() be sufficient to allow the freeze
> > to happen, or do I need to add an explicit try_to_freeze()?
> 
> You need a try_to_freeze() - the process has to enter the refrigerator()
> function to be counted as frozen.

Even though it explicitly sleeps each time through the loop?  Hmmm...

> > Ah, and I probably need to use the same trick that mtd_blktrans_thread()
> > does to avoid having all my sleeps killed of by an errant signal:
> > 
> > 	spin_lock_irq(&current->sighand->siglock);
> > 	sigfillset(&current->blocked);
> > 	recalc_sigpending();
> > 	spin_unlock_irq(&current->sighand->siglock);
> > 
> > Or is such paranoia unnecessary?
> 
> Yeah. try_to_freeze() is a function now, so you can do something if
> (try_to_freeze()) goto sleep_again if you so desire.

If try_to_freeze() succeeds, do I need to clean up signal state?
It didn't look like it to me, but thought I should ask the expert!

My guess is that I can simply do:

	try_to_freeze();
	schedule_timeout_interruptible(HZ);

The schedule_timeout_interruptible() might return early, but if I
don't care about getting a shorter than expected sleep, I am OK,
right?  Besides, one would have to get a couple of very closely
spaced freeze_processes() calls for this to happen.  ;-)

						Thanx, Paul
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