linux-kernel - Re: [PATCH 1/2] sparc64: Implement local_irq_save

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Message-Id: <20100407.000625.203083228.davem@davemloft.net>
Date:	Wed, 07 Apr 2010 00:06:25 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	peterz@...radead.org
Cc:	mingo@...e.hu, acme@...hat.com, paulus@...ba.org, efault@....de,
	fweisbec@...il.com, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, sparclinux@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH 1/2] sparc64: Implement local_irq_save_nmi().

From: Peter Zijlstra <peterz@...radead.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.
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