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Date: Fri, 13 Jun 2008 00:28:08 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, arjan@infradead.org,
       andreas.herrmann3@amd.com
Subject: Re: [patch 6/6] x86: add c1e aware idle function
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On Fri, 13 Jun 2008 08:02:30 +0200 (CEST) Thomas Gleixner <tglx@linutronix.de> wrote:

> On Thu, 12 Jun 2008, Andrew Morton wrote:
> > On Thu, 12 Jun 2008 10:29:00 -0000
> > Thomas Gleixner <tglx@linutronix.de> wrote:
> > > +		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu);
> > > +		default_idle();
> > > +		local_irq_disable();
> > > +		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &cpu);
> > > +		local_irq_enable();
> > 
> > I worked it out!  It took me a while.
> > 
> > This function is called with local irqs disabled.
> > 
> > default_idle() is entered with local irqs disabled but returns with them
> > enabled.
> > 
> > clockevents_notify() is supposed to be called with local irqs disabled.
> > 
> > This functions returns with local irqs enabled.
> 
> Damn, you decoded my sekrit.

The wonders of the GPL.

> > Was I right?  None of any of that is documented anywhere.  But it should
> > be.
> 
> Yeah, needs a big comment. Will add one.
> 

Actually it need lots of little comments.  One at default_idle(), one at
clockevents_notify(), one at whatever-this-function-was.

Because "must be called with local irqs disabled" is as much a part of
a function's interface as "must be passed a foo* and an integer and
returns a bar*".  Ditto "must be called under zot_lock".  But people
often forget these things.

I guess kerneldoc should have a standard "call environment" template. 
Maybe it does, dunno.

Of course, WARN_ON(!irqs_disabled()) and WARN_ON(!spin_is_locked(foo))
is robust documentation.