linux-kernel - Re: [PATCH] drivers/acpi/processor

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Date:	Wed, 14 Mar 2012 17:04:41 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Julia Lawall <Julia.Lawall@...6.fr>
CC:	Len Brown <lenb@...nel.org>, kernel-janitors@...r.kernel.org,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	Julia Lawall <julia@...u.dk>,
	Deepthi Dharwar <deepthi@...ux.vnet.ibm.com>,
	Venkatesh Pallipadi <venki@...gle.com>, trenn@...e.de,
	bhelgaas@...gle.com
Subject: Re: [PATCH] drivers/acpi/processor_driver.c: add missing kfree

On 03/10/2012 10:35 PM, Julia Lawall wrote:

> From: Julia Lawall <julia@...u.dk>
> 
> The function acpi_processor_add is stored in the ops.add field of a
> acpi_driver structure.  This function is then called in
> acpi_bus_driver_init.  On failure, this function clears the field
> device->driver_data, but does not free its contents.  Thus the free has to
> be done by the add function.  In acpi_processor_add, the corresponding
> value is pr.  This value is currently freed on failure before storing it in
> device->driver_data, but not after.  This free is added in the error
> handling code at the end of the function.  The static global variable


"static global variable"?? never heard that one before ;-)
Maybe you meant "per_cpu variable processors"..

> processors is also cleared so that it does not refer to a dangling pointer.
> processor_device_array is cleared as well.
> 
> Signed-off-by: Julia Lawall <julia@...u.dk>
> 
> ---
> This is only compile tested.  In particular, I don't know if it is correct
> to add per_cpu(processor_device_array, pr->id) = NULL;.


No, you shouldn't set it to NULL. processor_device_array was added to check
for buggy BIOSes and return gracefully. Check commit cd8e2b48d (and also the
bugzilla link in that commit).

To have a robust check for buggy BIOSes, we must let it be as it is, even if
it is a stale pointer. That way we can still catch subsequent calls to this
function with the same acpi id (because of a buggy BIOS) and take appropriate
actions.

Other than that, the patch looks good to me.

Regards,
Srivatsa S. Bhat
IBM Linux Technology Center

>  It has nothing to
> do with pr, but it looks like stale information in the case of a failure.
> 
>  drivers/acpi/processor_driver.c |   12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/acpi/processor_driver.c b/drivers/acpi/processor_driver.c
> index 2801b41..9bb0017 100644
> --- a/drivers/acpi/processor_driver.c
> +++ b/drivers/acpi/processor_driver.c
> @@ -536,8 +536,8 @@ static int __cpuinit acpi_processor_add(struct acpi_device *device)
>  		return -ENOMEM;
> 
>  	if (!zalloc_cpumask_var(&pr->throttling.shared_cpu_map, GFP_KERNEL)) {
> -		kfree(pr);
> -		return -ENOMEM;
> +		result = -ENOMEM;
> +		goto err_free_pr;
>  	}
> 
>  	pr->handle = device->handle;
> @@ -577,7 +577,7 @@ static int __cpuinit acpi_processor_add(struct acpi_device *device)
>  	dev = get_cpu_device(pr->id);
>  	if (sysfs_create_link(&device->dev.kobj, &dev->kobj, "sysdev")) {
>  		result = -EFAULT;
> -		goto err_free_cpumask;
> +		goto err_clear_processors;
>  	}
> 
>  	/*
> @@ -595,9 +595,13 @@ static int __cpuinit acpi_processor_add(struct acpi_device *device)
> 
>  err_remove_sysfs:
>  	sysfs_remove_link(&device->dev.kobj, "sysdev");
> +err_clear_processors:
> +	per_cpu(processors, pr->id) = NULL;
> +	per_cpu(processor_device_array, pr->id) = NULL;
>  err_free_cpumask:
>  	free_cpumask_var(pr->throttling.shared_cpu_map);
> -
> +err_free_pr:
> +	kfree(pr);
>  	return result;
>  }
> 
> 

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