Re: INFO: REPRODUCED: memory leak in gpio device in 6.2-rc6

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxx>]

On Mon, Feb 20, 2023 at 02:10:00PM +0100, Mirsad Todorovac wrote:
> On 2/16/23 15:16, Bartosz Golaszewski wrote:

...

> As Mr. McKenney once said, a bunch of monkeys with keyboard could
> have done it in a considerable number of trials and errors ;-)
> 
> But here I have something that could potentially leak as well. I could not devise a
> reproducer due to the leak being lightly triggered only in extreme memory contention.
> 
> See it for yourself:
> 
> drivers/gpio/gpio-sim.c:
>  301 static int gpio_sim_setup_sysfs(struct gpio_sim_chip *chip)
>  302 {
>  303         struct device_attribute *val_dev_attr, *pull_dev_attr;
>  304         struct gpio_sim_attribute *val_attr, *pull_attr;
>  305         unsigned int num_lines = chip->gc.ngpio;
>  306         struct device *dev = chip->gc.parent;
>  307         struct attribute_group *attr_group;
>  308         struct attribute **attrs;
>  309         int i, ret;
>  310
>  311         chip->attr_groups = devm_kcalloc(dev, sizeof(*chip->attr_groups),
>  312                                          num_lines + 1, GFP_KERNEL);
>  313         if (!chip->attr_groups)
>  314                 return -ENOMEM;
>  315
>  316         for (i = 0; i < num_lines; i++) {
>  317                 attr_group = devm_kzalloc(dev, sizeof(*attr_group), GFP_KERNEL);
>  318                 attrs = devm_kcalloc(dev, GPIO_SIM_NUM_ATTRS, sizeof(*attrs),
>  319                                      GFP_KERNEL);
>  320                 val_attr = devm_kzalloc(dev, sizeof(*val_attr), GFP_KERNEL);
>  321                 pull_attr = devm_kzalloc(dev, sizeof(*pull_attr), GFP_KERNEL);
>  322                 if (!attr_group || !attrs || !val_attr || !pull_attr)
>  323                         return -ENOMEM;
>  324
>  325                 attr_group->name = devm_kasprintf(dev, GFP_KERNEL,
>  326                                                   "sim_gpio%u", i);
>  327                 if (!attr_group->name)
>  328                         return -ENOMEM;
> 
> Apparently, if the memory allocation only partially succeeds, in the theoretical case
> that the system is close to its kernel memory exhaustion, `return -ENOMEM` would not
> free the partially succeeded allocs, would it?
> 
> To explain it better, I tried a version that is not yet full doing "all or nothing"
> memory allocation for the gpio-sim driver, because I am not that familiar with the
> driver internals.

devm_*() mean that the resource allocation is made in a managed manner, so when
it's done, it will be freed automatically.

The question is: is the lifetime of the attr_groups should be lesser or the
same as chip->gc.parent? Maybe it's incorrect to call devm_*() in the first place?

Or maybe the chip->gc.parent should be changed to something else (actual GPIO
device, but then it's unclear how to provide the attributes in non-racy way.

-- 
With Best Regards,
Andy Shevchenko