linux-kernel - Re: [PATCH] parisc: avoid WARNING: at kernel/cpu/idle.c:96

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Date:	Sat, 18 May 2013 21:40:55 +0200
From:	Helge Deller <deller@....de>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
CC:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-parisc@...r.kernel.org,
	John David Anglin <dave.anglin@...l.net>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] parisc: avoid WARNING: at kernel/cpu/idle.c:96

On 05/17/2013 09:25 PM, Srivatsa S. Bhat wrote:
> On 05/09/2013 02:35 AM, James Bottomley wrote:
>> On Wed, 2013-05-08 at 22:42 +0200, Helge Deller wrote:
>>> We need to enable local irqs to avoid this runtime warning.
>>>
>>> Signed-off-by: Helge Deller <deller@....de>
>>>
>>> diff --git a/arch/parisc/kernel/process.c b/arch/parisc/kernel/process.c
>>> index 55f92b6..2840d43 100644
>>> --- a/arch/parisc/kernel/process.c
>>> +++ b/arch/parisc/kernel/process.c
>>> @@ -286,3 +286,8 @@ void *dereference_function_descriptor(void *ptr)
>>>  	return ptr;
>>>  }
>>>  #endif
>>> +
>>> +void arch_cpu_idle(void)
>>> +{
>>> +	local_irq_enable();
>>
>> This is definitely wrong.  we'd need at least a cpu_relax() in there.
>> Without that the cpu will bounce around in the idle loop.  I'd advise
>> that we simply keep the default cpu_idle_poll().
>>
>> However, this looks like a kernel bug to me in cpu_idle_loop()?  not
>> something we should be working around in the arch code.
>>
>> Thomas, what's going on here?  It looks like you can never avoid the
>> WARN_ON_ONCE if you don't provide any arch specific idle functions.  If
>> you wish to allow this case then the correct patch (keeping the WARN_ON)
>> would appear to be this one.
>>
>> James
>>
>> ----
>> diff --git a/kernel/cpu/idle.c b/kernel/cpu/idle.c
>> index 8b86c0c..829e41f 100644
>> --- a/kernel/cpu/idle.c
>> +++ b/kernel/cpu/idle.c
>> @@ -56,6 +56,7 @@ void __weak arch_cpu_idle_dead(void) { }
>>  void __weak arch_cpu_idle(void)
>>  {
>>  	cpu_idle_force_poll = 1;
>> +	local_irq_enable();
>>  }
>>
>>  /*
>>
> 
> This patch looks like the correct fix to me.
> 
> Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>

Thanks Srivatsa!

I can push it through the parisc tree if nobody objects...

Helge
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