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Subject[Bug? Report] kref problem
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Hello Greg,

I've hit on a kref problem Please, glance at the attached test module.

The idea of the test is to create 2 kobjects (a and b), create dir A
with kobject A, and dir B with kobject B, so that A is B's parent. E.g.,
we'll have /sys/A/B.

I see the following output of the test:

a inited, kref 1
b inited, kref 1
dir A created, A kref 1, B kref 1
dir B created, A kref 1, B kref 1
b_release
a_release
kobj B put, A kref 0, B kref 0
kobj A put, A kref -1, B kref 0


So what I don't like is this "A kref -1". Why when I remove directory B,
kobj a is released? For me it looks like a bug.

The kernel is 2.6.16-rc6.

Thanks.

--
Best Regards,
Artem B. Bityuckiy,
St.-Petersburg, Russia.
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kobject.h>
#include <linux/stat.h>

static void a_release(struct kobject *kobj);

static struct kobj_type a_ktype = {
.release = a_release
};
static void b_release(struct kobject *kobj);

static struct kobj_type b_ktype = {
.release = b_release
};
struct my_obj_a
{
struct kobject kobj;
} a;
struct my_obj_b
{
struct kobject kobj;
} b;
static __init int test_init(void)
{
int err;
kobject_init(&a.kobj);
a.kobj.ktype = &a_ktype;
err = kobject_set_name(&a.kobj, "A");
if (err)
return err;
printk("a inited, kref %d\n", atomic_read(&a.kobj.kref.refcount));
kobject_init(&b.kobj);
b.kobj.ktype = &b_ktype;
b.kobj.parent = &a.kobj;
err = kobject_set_name(&b.kobj, "B");
if (err)
goto out_a;
printk("b inited, kref %d\n", atomic_read(&b.kobj.kref.refcount));
err = sysfs_create_dir(&a.kobj);
if (err)
goto out_b;
printk("dir A created, A kref %d, B kref %d\n",
atomic_read(&a.kobj.kref.refcount), atomic_read(&b.kobj.kref.refcount));
err = sysfs_create_dir(&b.kobj);
if (err)
goto out_a_dir;
printk("dir B created, A kref %d, B kref %d\n",
atomic_read(&a.kobj.kref.refcount), atomic_read(&b.kobj.kref.refcount));
kobject_put(&b.kobj);
printk("kobj B put, A kref %d, B kref %d\n",
atomic_read(&a.kobj.kref.refcount), atomic_read(&b.kobj.kref.refcount));

kobject_put(&a.kobj);
printk("kobj A put, A kref %d, B kref %d\n",
atomic_read(&a.kobj.kref.refcount), atomic_read(&b.kobj.kref.refcount));

return 0;

out_a_dir:
sysfs_remove_dir(&a.kobj);
out_b:
kobject_put(&b.kobj);
out_a:
kobject_put(&a.kobj);
return err;
}
module_init(test_init);
static void a_release(struct kobject *kobj)
{
struct my_obj_a *a;
printk("%s\n", __FUNCTION__);
a = container_of(kobj, struct my_obj_a, kobj);
sysfs_remove_dir(&a->kobj);
}
static void b_release(struct kobject *kobj)
{
struct my_obj_b *b;
printk("%s\n", __FUNCTION__);
b = container_of(kobj, struct my_obj_b, kobj);
sysfs_remove_dir(&b->kobj);
}
static __exit void test_exit(void)
{
}
module_exit(test_exit);
MODULE_VERSION("1");
MODULE_DESCRIPTION("kref test");
MODULE_AUTHOR("Artem B. Bityutskiy");
MODULE_LICENSE("GPL");
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