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

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Date:	Fri, 02 Feb 2007 09:13:46 +1100
From:	Nigel Cunningham <nigel@...el.suspend2.net>
To:	paulmck@...ux.vnet.ibm.com
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

Hi.

On Wed, 2007-01-31 at 21:46 -0800, Paul E. McKenney wrote:
> 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...

Yes. Sleeping isn't enough - we have to be sure it won't wake up and
perform work at inappropriate times (we don't know what process X might
do if it did wake; the result could be an inconsistent image). It
therefore needs to enter the refrigerator function so that the freezer
code can ensure it remains inactive until the suspend-to-whatever cycle
is complete.

> > > 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!

No, you don't need to. We have recalc_sigpending() in the refrigerator
function.

> 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.  ;-)

Yes, that looks good to me.

Regards,

Nigel

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