[patch 00/12] arm: raw_spinlock annotations

[tglx@linutronix.de (Thomas Gleixner)]

On Tue, 19 Oct 2010, Arnd Bergmann wrote:

> On Tuesday 19 October 2010 22:03:32 Thomas Gleixner wrote:
> > On Tue, 19 Oct 2010, Russell King - ARM Linux wrote:
> > 
> > > On Tue, Oct 19, 2010 at 05:26:45PM +0200, Arnd Bergmann wrote:
> > > > On Tuesday 19 October 2010, Uwe Kleine-K?nig wrote:
> > > > > While cleaning up my repo I refound the patches and rebased them on top
> > > > > of today's Linus' tree and only needed to fix up the l2x0_lock patch as
> > > > > in the meantime a new usage hit mainline.
> > > > 
> > > > The patches all look harmless, but none of them has any information on
> > > > why the particular locks need to be raw_spin_lock. Ideally a raw spinlock
> > > > should be the absolute exception, and IMHO should have a comment in front
> > > > of it why it is special.
> > > 
> > > Or at least explained in the patch description.
> > > 
> > > For instance, can someone explain why the lock for leds and gpio stuff
> > > on Footbridge needs to be converted?  What is the original problem?
> > > More importantly, what is the criteria for using a raw spinlock instead
> > > of a normal spinlock?
> > 
> > raw_spinlock is still a spinlock when PREEMPT_RT is enabled, mere
> > spinlocks become magically "sleeping" spinlocks (aka. PI aware
> > rtmutexes)
> 
> I think we all understood that part of the series description.
> 
> > Vs. the patches: IIRC, it was all fallout from running -rt, but that
> > needs to be looked at case by case. Some of those are obvious as they
> > are called deep down in atomic irq disabled code, but others might be
> > just due to laziness reasons.
> 
> Not as obvious as you'd think. The explanation "called in atomic irq
> disabled code" makes sense, but I hadn't thought of that before -- I had
> expected all that code to use IRQ threads in case of PREEMPT_RT.
> 
> Requiring a comment there would probably eliminate the laziness issues,
> adding a comment that you can't be bothered to do the right fix won't
> help getting a patch merged, so ideally you'd end up with a better
> solution getting merged.

I know, that's why I'm not pressuring that issue. It needs work and
looking at the code and context. That few lines can happily live in
-rt for now. We have bigger fish to fry there.

Thanks,

	tglx