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

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Message-ID: <5196843B.8060807@linux.vnet.ibm.com>
Date:	Sat, 18 May 2013 00:55:47 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Thomas Gleixner <tglx@...utronix.de>
CC:	Helge Deller <deller@....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 05/09/2013 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>

Regards,
Srivatsa S. Bhat


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