linux-kernel - Re: [PATCH 1/3] powerpc: Fixup hard_irq

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Message-Id: <1178786662.14928.229.camel@localhost.localdomain>
Date:	Thu, 10 May 2007 18:44:22 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
Cc:	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH 1/3] powerpc: Fixup hard_irq_disable semantics

On Thu, 2007-05-10 at 09:44 +0200, Geert Uytterhoeven wrote:
> On Thu, 10 May 2007, Benjamin Herrenschmidt wrote:
> > This patch renames the raw hard_irq_{enable,disable} into
> > __hard_irq_{enable,disable} and introduces a higher level
> > hard_irq_disable() function that can be used by any code
> > to enforce that IRQs are fully disabled, not only lazy
> > disabled.
> 
> Why did you rename hard_irq_enable() too?
> 
> Isn't it more logical to have high-level hard_irq_disable() and
> hard_irq_enable(), and a special low-level __hard_irq_disable()?

Not really. If you see my subsequent patch, the idea is to introduce a
single generic hard_irq_disable() which is meant to be called with
irqs already disabled (that is within a local_irq_disable section) to
enforce that if the arch does lazy disabling, it gets hard disabled
at this point.

If we start adding hard_irq_enable() we end up in a can of worms:

 - Do we want all the full set of save/restore etc... ?
 - What if somebody does hard_enable while we are soft-disabled
   -and- have been hard disabled because of a pending interrupt ?
 - What's the point ? :-)

So overall, I want to keep the semantics as simple as they can be. Maybe
I can even add some WARN_ON() to make sure we are in a
local_irq_disable'd section even in the generic one instead of just a
NOP to enfore that.

Cheers,
Ben.


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