Re: [PATCH v2 6/6] hwmon: pmbus: use more devres helpers

Guenter Roeck
2020-07-02T14:29:37Z

On 7/2/20 5:44 AM, Greg Kroah-Hartman wrote:
> On Mon, Jun 29, 2020 at 08:50:08AM +0200, Bartosz Golaszewski wrote:
>> From: Bartosz Golaszewski <bgolaszewski@baylibre.com>
>>
>> Shrink pmbus code by using devm_hwmon_device_register_with_groups()
>> and devm_krealloc() instead of their non-managed variants.
>>
>> Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
>> ---
>> drivers/hwmon/pmbus/pmbus_core.c | 28 +++++++++-------------------
>> 1 file changed, 9 insertions(+), 19 deletions(-)
>>
>> diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
>> index a420877ba533..225d0ac162c7 100644
>> --- a/drivers/hwmon/pmbus/pmbus_core.c
>> +++ b/drivers/hwmon/pmbus/pmbus_core.c
>> @@ -1022,9 +1022,9 @@ static int pmbus_add_attribute(struct pmbus_data *data, struct attribute *attr)
>> {
>> if (data->num_attributes >= data->max_attributes - 1) {
>> int new_max_attrs = data->max_attributes + PMBUS_ATTR_ALLOC_SIZE;
>> - void *new_attrs = krealloc(data->group.attrs,
>> - new_max_attrs * sizeof(void *),
>> - GFP_KERNEL);
>> + void *new_attrs = devm_krealloc(data->dev, data->group.attrs,
>> + new_max_attrs * sizeof(void *),
>> + GFP_KERNEL);
>
> dynamic sysfs attributes in a devm-allocated chunk of memory? What
> could go wrong...
>

You mean that the memory might be removed before the attributes
are removed ? Hmm, but that isn't different to the current implementation.
The hwmon device is removed first (removing the sysfs attributes),
followed by the kfree. Are you saying this is not safe ?
Pretty much all code which allocates memory for struct attribute
is doing the same, so that would be a problem throughout the kernel.

> Anyway, is this the only in-kernel user that you could find for this
> function? If so, it feels like it's a lot of extra work for no real
> gain.
>
And I was so happy that I'd be able to get rid of pmbus_do_remove()
subsequently. But then I can also use devm_add_action() and have it
call kfree(), with the same result. Given that, if hwmon would really
be the only user, we can live without it.

Guenter