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

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Date:	Wed, 14 Mar 2012 13:32:06 +0100 (CET)
From:	Julia Lawall <julia.lawall@...6.fr>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
cc:	Julia Lawall <Julia.Lawall@...6.fr>, 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 Wed, 14 Mar 2012, Srivatsa S. Bhat wrote:

> 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.

Thanks for the feedback.  Just to be clear, I should keep

+err_clear_processors:
+       per_cpu(processors, pr->id) = NULL;

and just drop:

+       per_cpu(processor_device_array, pr->id) = NULL;

julia

>
> 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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