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

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxx>]

On Tue, Feb 21, 2023 at 02:52:38PM +0100, Mirsad Goran Todorovac wrote:
> On 20. 02. 2023. 14:43, Andy Shevchenko wrote:
> > 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.
> 
> Didn't see that one coming ... :-/ "buzzing though the bush ..."
> 
> > 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?
> 
> Bona fide said, I hope that automatic deallocation does things in the right order.
> I've realised that devm_kzalloc() calls devm_kmalloc() that registers allocations on
> a per driver list. But I am not sure how chip->gc was allocated?
> 
> Here is said it is allocated in drivers/gpio/gpio-sim.c:386 in gpio_sim_add_bank(),
> as a part of
> 
> 	struct gpio_sim_chip *chip;
> 	struct gpio_chip *gc;
> 
> 	gc = &chip->gc;
> 
> and gc->parent is set to
> 
> 	gc->parent = dev;
> 
> in line 420, which appears called before gpio_sim_setup_sysfs() and the lines above.
> 
> If I understood well, automatic deallocation on unloading the driver goes
> in the reverse order, so lifetime of chip appears to be longer than attr_groups,
> but I am really not that good at this ...

So, the device is instantiated by platform_device_register_full().

It should gone with the platform_device_unregister().

In case of CONFIG_DEBUG_KOBJECT_RELEASE=y the ->release() can be called
asynchronously.

So, there are following questions:
- is the put_device() is actually called?
- is the above mentioned option is set to Y?
- if it's in Y, does kmemleak take it into account?
- if no, do you get anything new in `dmesg` when enable it?

> > 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
> Really, dunno. I have to repeat that my learning curve cannot adapt so quickly.
> 
> I merely gave the report of KMEMLEAK, otherwise I am not a Linux kernel
> device expert nor would be appropriate to try the craft not earned ;-)

-- 
With Best Regards,
Andy Shevchenko