linux-kernel - Re: [PATCH RFC] acpi: Fix unprotected smp_processor_id() in acpi_processor_cst_has

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Date:	Tue, 28 Feb 2012 11:43:20 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	paulmck@...ux.vnet.ibm.com
CC:	deepthi@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	lenb@...nel.org, linux-acpi@...r.kernel.org
Subject: Re: [PATCH RFC] acpi: Fix unprotected smp_processor_id() in acpi_processor_cst_has_changed()

On 02/24/2012 02:28 AM, Paul E. McKenney wrote:

> The acpi_processor_cst_has_changed() function is invoked from a
> CPU_ONLINE or CPU_DEAD function, which might well execute on CPU 0
> even though the CPU being hotplugged is some other CPU.  In addition,
> acpi_processor_cst_has_changed() invokes smp_processor_id() without
> protection, resulting in splats when onlining CPUs.
> 
> This commit therefore changes the smp_processor_id() to pr->id, as is
> used elsewhere in the code, for example, in acpi_processor_add().
> 
> This works for me, but I don't claim to understand ACPI.
> 
> Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
>


This looks like the right fix to me, observing the disparity between what
the comment says (and hence what was intended) vs what the code originally
did.

Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>

 
> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> index 0e8e2de..9e57b06 100644
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -1159,8 +1159,7 @@ int acpi_processor_cst_has_changed(struct acpi_processor *pr)
>  	 * to make the code that updates C-States be called once.
>  	 */
> 
> -	if (smp_processor_id() == 0 &&
> -			cpuidle_get_driver() == &acpi_idle_driver) {
> +	if (pr->id == 0 && cpuidle_get_driver() == &acpi_idle_driver) {
> 
>  		cpuidle_pause_and_lock();
>  		/* Protect against cpu-hotplug */
> 

 
Regards,
Srivatsa S. Bhat

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