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

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Date:	Wed, 08 May 2013 14:05:34 -0700
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Helge Deller <deller@....de>
Cc:	linux-parisc@...r.kernel.org,
	John David Anglin <dave.anglin@...l.net>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] parisc: avoid WARNING: at kernel/cpu/idle.c:96

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();
 }
 
 /*


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