Date: Mon, 13 Sep 2004 09:10:22 +0100
From: Russell King <rmk+lkml@arm.linux.org.uk>
To: "David S. Miller" <davem@davemloft.net>
Cc: akpm@osdl.org, spyro@f2s.com, linux390@de.ibm.com,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH] irq_enter/irq_exit consolidation
Message-ID: <20040913091022.A27423@flint.arm.linux.org.uk>
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	spyro@f2s.com, linux390@de.ibm.com, linux-kernel@vger.kernel.org
References: <20040912112554.GA32550@lst.de> <20040912124448.A13676@flint.arm.linux.org.uk> <20040912155720.34b188d7.davem@davemloft.net>
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In-Reply-To: <20040912155720.34b188d7.davem@davemloft.net>; from davem@davemloft.net on Sun, Sep 12, 2004 at 03:57:20PM -0700
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On Sun, Sep 12, 2004 at 03:57:20PM -0700, David S. Miller wrote:
> On Sun, 12 Sep 2004 12:44:48 +0100
> Russell King <rmk+lkml@arm.linux.org.uk> wrote:
> 
> > This guarantee must also exist on every other architecture, otherwise:
> > 
> > > ===== include/linux/hardirq.h 1.1 vs edited =====
> > > --- 1.1/include/linux/hardirq.h	2004-09-08 08:32:57 +02:00
> > > +++ edited/include/linux/hardirq.h	2004-09-11 21:26:28 +02:00
> > > +#define irq_exit()						\
> > > +do {								\
> > > +	preempt_count() -= IRQ_EXIT_OFFSET;			\
> > 
> > would be buggy - it's an inherently non-atomic operation.
> 
> It works out actually, if we take an interrupt in the middle
> of the operation, that's fine because the preemption count
> will be precisely the same as we first read it by the time
> we return from that interrupt, work out some example cases
> as I think that makes it easier to understand.

I realise that, and it's precisely why I wrote the sentence following
the one you quoted above.

However, ARM ain't buggy whatever.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 PCMCIA      - http://pcmcia.arm.linux.org.uk/
                 2.6 Serial core
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