Re: [PATCH, v4] hwmon: coretemp: use list instead of fixed size array for temp data

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On Tue, 2012-05-08 at 06:49 -0400, Kirill A. Shutemov wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> 
> Let's rework code to allow arbitrary number of cores on a CPU, not
> limited by hardcoded array size.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> ---
>  v4:
>    - address issues pointed by Guenter Roeck;
>  v3:
>    - drop redundant refcounting and checks;
>  v2:
>    - fix NULL pointer dereference. Thanks to R, Durgadoss;
>    - use mutex instead of spinlock for list locking.
> ---

Hi Kirill,

unfortunately now we have another race condition :(. See below ...

>  drivers/hwmon/coretemp.c |  119 ++++++++++++++++++++++++++++++----------------
>  1 files changed, 78 insertions(+), 41 deletions(-)
> 
> diff --git a/drivers/hwmon/coretemp.c b/drivers/hwmon/coretemp.c
> index b9d5123..602bdc8 100644
> --- a/drivers/hwmon/coretemp.c
> +++ b/drivers/hwmon/coretemp.c
> @@ -36,6 +36,7 @@
>  #include <linux/cpu.h>
>  #include <linux/pci.h>
>  #include <linux/smp.h>
> +#include <linux/list.h>
>  #include <linux/moduleparam.h>
>  #include <asm/msr.h>
>  #include <asm/processor.h>
> @@ -52,11 +53,9 @@ module_param_named(tjmax, force_tjmax, int, 0444);
>  MODULE_PARM_DESC(tjmax, "TjMax value in degrees Celsius");
>  
>  #define BASE_SYSFS_ATTR_NO	2	/* Sysfs Base attr no for coretemp */
> -#define NUM_REAL_CORES		32	/* Number of Real cores per cpu */
>  #define CORETEMP_NAME_LENGTH	17	/* String Length of attrs */
>  #define MAX_CORE_ATTRS		4	/* Maximum no of basic attrs */
>  #define TOTAL_ATTRS		(MAX_CORE_ATTRS + 1)
> -#define MAX_CORE_DATA		(NUM_REAL_CORES + BASE_SYSFS_ATTR_NO)
>  
>  #define TO_PHYS_ID(cpu)		(cpu_data(cpu).phys_proc_id)
>  #define TO_CORE_ID(cpu)		(cpu_data(cpu).cpu_core_id)
> @@ -82,6 +81,8 @@ MODULE_PARM_DESC(tjmax, "TjMax value in degrees Celsius");
>   * @valid: If this is 1, the current temperature is valid.
>   */
>  struct temp_data {
> +	struct list_head list;
> +	int id;
>  	int temp;
>  	int ttarget;
>  	int tjmax;
> @@ -101,7 +102,8 @@ struct temp_data {
>  struct platform_data {
>  	struct device *hwmon_dev;
>  	u16 phys_proc_id;
> -	struct temp_data *core_data[MAX_CORE_DATA];
> +	struct list_head temp_data_list;
> +	struct mutex temp_data_lock;
>  	struct device_attribute name_attr;
>  };
>  
> @@ -114,6 +116,20 @@ struct pdev_entry {
>  static LIST_HEAD(pdev_list);
>  static DEFINE_MUTEX(pdev_list_mutex);
>  
> +static struct temp_data *get_temp_data(struct platform_data *pdata, int id)
> +{
> +	struct temp_data *tdata;
> +
> +	mutex_lock(&pdata->temp_data_lock);
> +	list_for_each_entry(tdata, &pdata->temp_data_list, list)
> +		if (tdata->id == id)
> +			goto out;
> +	tdata = NULL;
> +out:
> +	mutex_unlock(&pdata->temp_data_lock);
> +	return tdata;
> +}
> +
>  static ssize_t show_name(struct device *dev,
>  			struct device_attribute *devattr, char *buf)
>  {
> @@ -125,7 +141,7 @@ static ssize_t show_label(struct device *dev,
>  {
>  	struct sensor_device_attribute *attr = to_sensor_dev_attr(devattr);
>  	struct platform_data *pdata = dev_get_drvdata(dev);
> -	struct temp_data *tdata = pdata->core_data[attr->index];
> +	struct temp_data *tdata = get_temp_data(pdata, attr->index);
>  
>  	if (tdata->is_pkg_data)
>  		return sprintf(buf, "Physical id %u\n", pdata->phys_proc_id);
> @@ -139,7 +155,7 @@ static ssize_t show_crit_alarm(struct device *dev,
>  	u32 eax, edx;
>  	struct sensor_device_attribute *attr = to_sensor_dev_attr(devattr);
>  	struct platform_data *pdata = dev_get_drvdata(dev);
> -	struct temp_data *tdata = pdata->core_data[attr->index];
> +	struct temp_data *tdata = get_temp_data(pdata, attr->index);
>  
>  	rdmsr_on_cpu(tdata->cpu, tdata->status_reg, &eax, &edx);
>  
> @@ -151,8 +167,9 @@ static ssize_t show_tjmax(struct device *dev,
>  {
>  	struct sensor_device_attribute *attr = to_sensor_dev_attr(devattr);
>  	struct platform_data *pdata = dev_get_drvdata(dev);
> +	struct temp_data *tdata = get_temp_data(pdata, attr->index);
>  
> -	return sprintf(buf, "%d\n", pdata->core_data[attr->index]->tjmax);
> +	return sprintf(buf, "%d\n", tdata->tjmax);
>  }
>  
>  static ssize_t show_ttarget(struct device *dev,
> @@ -160,8 +177,9 @@ static ssize_t show_ttarget(struct device *dev,
>  {
>  	struct sensor_device_attribute *attr = to_sensor_dev_attr(devattr);
>  	struct platform_data *pdata = dev_get_drvdata(dev);
> +	struct temp_data *tdata = get_temp_data(pdata, attr->index);
>  
> -	return sprintf(buf, "%d\n", pdata->core_data[attr->index]->ttarget);
> +	return sprintf(buf, "%d\n", tdata->ttarget);
>  }
>  
>  static ssize_t show_temp(struct device *dev,
> @@ -170,7 +188,7 @@ static ssize_t show_temp(struct device *dev,
>  	u32 eax, edx;
>  	struct sensor_device_attribute *attr = to_sensor_dev_attr(devattr);
>  	struct platform_data *pdata = dev_get_drvdata(dev);
> -	struct temp_data *tdata = pdata->core_data[attr->index];
> +	struct temp_data *tdata = get_temp_data(pdata, attr->index);
>  
>  	mutex_lock(&tdata->update_lock);
>  
> @@ -423,7 +441,7 @@ static struct temp_data __cpuinit *init_temp_data(unsigned int cpu,
>  	return tdata;
>  }
>  
> -static int __cpuinit create_core_data(struct platform_device *pdev,
> +static int __cpuinit create_temp_data(struct platform_device *pdev,
>  				unsigned int cpu, int pkg_flag)
>  {
>  	struct temp_data *tdata;
> @@ -440,9 +458,6 @@ static int __cpuinit create_core_data(struct platform_device *pdev,
>  	 */
>  	attr_no = pkg_flag ? 1 : TO_ATTR_NO(cpu);
>  
> -	if (attr_no > MAX_CORE_DATA - 1)
> -		return -ERANGE;
> -
>  	/*
>  	 * Provide a single set of attributes for all HT siblings of a core
>  	 * to avoid duplicate sensors (the processor ID and core ID of all
> @@ -450,7 +465,8 @@ static int __cpuinit create_core_data(struct platform_device *pdev,
>  	 * Skip if a HT sibling of this core is already registered.
>  	 * This is not an error.
>  	 */
> -	if (pdata->core_data[attr_no] != NULL)
> +	tdata = get_temp_data(pdata, attr_no);
> +	if (tdata)
>  		return 0;
>  
>  	tdata = init_temp_data(cpu, pkg_flag);
> @@ -480,16 +496,23 @@ static int __cpuinit create_core_data(struct platform_device *pdev,
>  		}
>  	}
>  
> -	pdata->core_data[attr_no] = tdata;
> +	tdata->id = attr_no;
> +
> +	mutex_lock(&pdata->temp_data_lock);
> +	list_add(&tdata->list, &pdata->temp_data_list);
> +	mutex_unlock(&pdata->temp_data_lock);
>  
>  	/* Create sysfs interfaces */
>  	err = create_core_attrs(tdata, &pdev->dev, attr_no);
>  	if (err)
> -		goto exit_free;
> +		goto exit_list_del;
>  
>  	return 0;
> +exit_list_del:
> +	mutex_lock(&pdata->temp_data_lock);
> +	list_del(&tdata->list);
> +	mutex_unlock(&pdata->temp_data_lock);
>  exit_free:
> -	pdata->core_data[attr_no] = NULL;
>  	kfree(tdata);
>  	return err;
>  }
> @@ -502,23 +525,20 @@ static void __cpuinit coretemp_add_core(unsigned int cpu, int pkg_flag)
>  	if (!pdev)
>  		return;
>  
> -	err = create_core_data(pdev, cpu, pkg_flag);
> +	err = create_temp_data(pdev, cpu, pkg_flag);
>  	if (err)
>  		dev_err(&pdev->dev, "Adding Core %u failed\n", cpu);
>  }
>  
> -static void coretemp_remove_core(struct platform_data *pdata,
> -				struct device *dev, int indx)
> +static void coretemp_remove_core(struct temp_data *tdata, struct device *dev)
>  {
>  	int i;
> -	struct temp_data *tdata = pdata->core_data[indx];
>  
>  	/* Remove the sysfs attributes */
>  	for (i = 0; i < tdata->attr_size; i++)
>  		device_remove_file(dev, &tdata->sd_attrs[i].dev_attr);
>  
> -	kfree(pdata->core_data[indx]);
> -	pdata->core_data[indx] = NULL;
> +	kfree(tdata);
>  }
>  
>  static int __devinit coretemp_probe(struct platform_device *pdev)
> @@ -536,6 +556,8 @@ static int __devinit coretemp_probe(struct platform_device *pdev)
>  		goto exit_free;
>  
>  	pdata->phys_proc_id = pdev->id;
> +	INIT_LIST_HEAD(&pdata->temp_data_list);
> +	mutex_init(&pdata->temp_data_lock);
>  	platform_set_drvdata(pdev, pdata);
>  
>  	pdata->hwmon_dev = hwmon_device_register(&pdev->dev);
> @@ -557,11 +579,22 @@ exit_free:
>  static int __devexit coretemp_remove(struct platform_device *pdev)
>  {
>  	struct platform_data *pdata = platform_get_drvdata(pdev);
> -	int i;
> +	struct temp_data *tdata;
>  
> -	for (i = MAX_CORE_DATA - 1; i >= 0; --i)
> -		if (pdata->core_data[i])
> -			coretemp_remove_core(pdata, &pdev->dev, i);
> +	for (;;) {
> +		mutex_lock(&pdata->temp_data_lock);
> +		if (!list_empty(&pdata->temp_data_list)) {
> +			tdata = list_first_entry(&pdata->temp_data_list,
> +					struct temp_data, list);
> +			list_del(&tdata->list);
> +		} else
> +			tdata = NULL;
> +		mutex_unlock(&pdata->temp_data_lock);
> +
> +		if (!tdata)
> +			break;
> +		coretemp_remove_core(tdata, &pdev->dev);
> +	}
>  
Unfortunately, that results in a race condition, since the tdata list
entry is gone before the attribute file is deleted.

I think you can still use list_for_each_entry_safe, only outside the
mutex, and remove the list entry at the end of coretemp_remove_core()
after deleting the attribute file. Just keep the code as it was, and
remove the list entry (mutex-protected) where core_data[] was set to
NULL.

>  	device_remove_file(&pdev->dev, &pdata->name_attr);
>  	hwmon_device_unregister(pdata->hwmon_dev);
> @@ -641,16 +674,18 @@ static void __cpuinit coretemp_device_remove(unsigned int cpu)
>  
>  static bool __cpuinit is_any_core_online(struct platform_data *pdata)
>  {
> -	int i;
> +	struct temp_data *tdata;
> +	bool ret = false;
>  
> -	/* Find online cores, except pkgtemp data */
> -	for (i = MAX_CORE_DATA - 1; i >= 0; --i) {
> -		if (pdata->core_data[i] &&
> -			!pdata->core_data[i]->is_pkg_data) {
> -			return true;
> +	mutex_lock(&pdata->temp_data_lock);
> +	list_for_each_entry(tdata, &pdata->temp_data_list, list) {
> +		if (!tdata->is_pkg_data) {

Actually, we don't need is_pkg_data anymore at all. Just test for
"tdata->id == 1" instead. That will simplify the code a bit.

> +			ret = true;
> +			break;
>  		}
>  	}
> -	return false;
> +	mutex_unlock(&pdata->temp_data_lock);
> +	return ret;
>  }
>  
>  static void __cpuinit get_core_online(unsigned int cpu)
> @@ -697,9 +732,10 @@ static void __cpuinit get_core_online(unsigned int cpu)
>  
>  static void __cpuinit put_core_offline(unsigned int cpu)
>  {
> -	int i, indx;
> +	int i, attr_no;
>  	struct platform_data *pdata;
>  	struct platform_device *pdev = coretemp_get_pdev(cpu);
> +	struct temp_data *tdata;
>  
>  	/* If the physical CPU device does not exist, just return */
>  	if (!pdev)
> @@ -707,14 +743,15 @@ static void __cpuinit put_core_offline(unsigned int cpu)
>  
>  	pdata = platform_get_drvdata(pdev);
>  
> -	indx = TO_ATTR_NO(cpu);
> +	attr_no = TO_ATTR_NO(cpu);
>  
> -	/* The core id is too big, just return */
> -	if (indx > MAX_CORE_DATA - 1)
> -		return;
> -
> -	if (pdata->core_data[indx] && pdata->core_data[indx]->cpu == cpu)
> -		coretemp_remove_core(pdata, &pdev->dev, indx);
> +	tdata = get_temp_data(pdata, attr_no);
> +	if (tdata && tdata->cpu == cpu) {
> +		mutex_lock(&pdata->temp_data_lock);
> +		list_del(&tdata->list);
> +		mutex_unlock(&pdata->temp_data_lock);
> +		coretemp_remove_core(tdata, &pdev->dev);

Same race condition as above here.

> +	}
>  
>  	/*
>  	 * If a HT sibling of a core is taken offline, but another HT sibling



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