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Date: Wed, 07 Apr 2010 00:06:25 -0700 (PDT)
Message-Id: <20100407.000625.203083228.davem@davemloft.net>
To: peterz@infradead.org
Cc: mingo@elte.hu, acme@redhat.com, paulus@samba.org, efault@gmx.de,
       fweisbec@gmail.com, tglx@linutronix.de, linux-kernel@vger.kernel.org,
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Subject: Re: [PATCH 1/2] sparc64: Implement local_irq_save_nmi().
From: David Miller <davem@davemloft.net>
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	<1270623146.5109.532.camel@twins>
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From: Peter Zijlstra <peterz@infradead.org>
Date: Wed, 07 Apr 2010 08:52:26 +0200

> On Tue, 2010-04-06 at 16:39 -0700, David Miller wrote:
>> @@ -49,6 +49,16 @@ static inline void raw_local_irq_disable(void)
>>  	);
>>  }
>>  
>> +static inline void raw_local_irq_disable_nmi(void)
>> +{
>> +	__asm__ __volatile__(
>> +		"wrpr	%0, %%pil"
>> +		: /* no outputs */
>> +		: "i" (PIL_NMI)
>> +		: "memory"
>> +	);
>> +}
>> +
> 
> Isn't this wrong when used from !NMI context?
> 
> Should this thing do something like:
> 
>   if (rdpr() < PIL_NORMAL_MAX)
>     wrpr(PIL_NORMAL_MAX);
> 
> so that it only disables IRQs, but doesn't enable NMIs.

It's immaterial, local_irq_restore() will do the right thing,
and it's ok to disable NMIs in these few cases I think.

I desperately want to avoid that "test and maybe change the
value %pil value we write" business, and honestly that's
the whole point of this exercise.