[RFC PATCH 1/3] eeprom: Add a simple EEPROM framework

Srinivas Kandagatla
2015-02-20T19:00:22Z

On 20/02/15 17:46, Russell King - ARM Linux wrote:
> On Thu, Feb 19, 2015 at 05:08:28PM +0000, Srinivas Kandagatla wrote:
>> +static struct class eeprom_class = {
>> + .name = "eeprom",
>> + .dev_groups = eeprom_dev_groups,
>> +};
>> +
>> +int eeprom_register(struct eeprom_device *eeprom)
>> +{
>> + int rval;
>> +
>> + if (!eeprom->regmap || !eeprom->size) {
>> + dev_err(eeprom->dev, "Regmap not found\n");
>> + return -EINVAL;
>> + }
>> +
>> + eeprom->id = ida_simple_get(&eeprom_ida, 0, 0, GFP_KERNEL);
>> + if (eeprom->id < 0)
>> + return eeprom->id;
>> +
>> + eeprom->edev.class = &eeprom_class;
>> + eeprom->edev.parent = eeprom->dev;
>> + eeprom->edev.of_node = eeprom->dev ? eeprom->dev->of_node : NULL;
>> + dev_set_name(&eeprom->edev, "eeprom%d", eeprom->id);
>> +
>> + device_initialize(&eeprom->edev);
>> +
>> + dev_dbg(&eeprom->edev, "Registering eeprom device %s\n",
>> + dev_name(&eeprom->edev));
>> +
>> + rval = device_add(&eeprom->edev);
>> + if (rval)
>> + return rval;
>> +
>> + mutex_lock(&eeprom_list_mutex);
>> + list_add(&eeprom->list, &eeprom_list);
>> + mutex_unlock(&eeprom_list_mutex);
>> +
>> + return 0;
>> +}
>> +EXPORT_SYMBOL(eeprom_register);
>> +
>> +int eeprom_unregister(struct eeprom_device *eeprom)
>> +{
>> + device_del(&eeprom->edev);
>> +
>> + mutex_lock(&eeprom_list_mutex);
>> + list_del(&eeprom->list);
>> + mutex_unlock(&eeprom_list_mutex);
>> +
>> + return 0;
>
> There's problems with this. "edev" is embedded into eeprom, and "edev"
> is a refcounted structure - it has a lifetime, and the lifetime of
> eeprom is thus determined by edev.
>
> What this means is that calling eeprom_unregister() and then freeing
> the eeprom structure is a potentially unsafe operation - the memory
> backing edev must only be freed when the release method for the
> struct device has been called.

Thats a good catch, Yes I see the issue.

Moving the struct eeprom_device allocation to eeprom core.c should
address this issue. This makes eeprom self contained and can safely free
the eeprom_device memory in eeprom_class.eeprom_release().

Will fix this in next version.

>
>> +struct eeprom_device {
>> + struct regmap *regmap;
>> + int stride;
>> + size_t size;
>> + struct device *dev;
>
> Failing to understand and address the driver model life time issues is
> a major blocker for this patch. Sorry.
>