On 2/21/23 16:39, Andy Shevchenko wrote:
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?
Hi, Andy,
Having set CONFIG_DEBUG_KOBJECT=y.
CONFIG_DEBUG_KOBJECT_RELEASE=y and CONFIG_DEBUG_OBJECTS_TIMERS=y disappear after "make olddefconfig"
So, I cannot tell about whether release() was called asynchronously, all I get is (after driver unload):
[ 810.989742] kobject: 'gpio-sim' (00000000251afa19): kobject_cleanup, parent 00000000447da7a7
[ 810.990216] kobject: 'gpio-sim' (00000000251afa19): auto cleanup kobject_del
[ 810.990674] kobject: 'gpio-sim' (00000000251afa19): auto cleanup 'remove' event
[ 810.991175] kobject: 'gpio-sim' (00000000251afa19): kobject_uevent_env
[ 810.991674] kobject: 'gpio-sim' (00000000251afa19): fill_kobj_path: path = '/bus/platform/drivers/gpio-sim'
[ 810.992154] kobject: 'gpio-sim' (00000000251afa19): calling ktype release
[ 810.992644] kobject: 'gpio-sim': free name
I am still trying to convince "make olddefconfig" to accept the above values he did not like :-/
Regards,
Mirsad
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 ;-)
--
Mirsad Goran Todorovac
Sistem inženjer
Grafički fakultet | Akademija likovnih umjetnosti
Sveučilište u Zagrebu
System engineer
Faculty of Graphic Arts | Academy of Fine Arts
University of Zagreb, Republic of Croatia
