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

Russell King - ARM Linux
2015-02-20T17:46:41Z

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.

> +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.

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