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SubjectBug in sysfs_break_active_protection()
Tejun:

It looks like there's a memory leak in sysfs_break_active_protection().
It and its companion routine do this:

struct kernfs_node *sysfs_break_active_protection(struct kobject *kobj,
const struct attribute *attr)
{
struct kernfs_node *kn;

kobject_get(kobj);
kn = kernfs_find_and_get(kobj->sd, attr->name);
if (kn)
kernfs_break_active_protection(kn);
return kn;
}

void sysfs_unbreak_active_protection(struct kernfs_node *kn)
{
struct kobject *kobj = kn->parent->priv;

kernfs_unbreak_active_protection(kn);
kernfs_put(kn);
kobject_put(kobj);
}

If kn is NULL then the kobject_get(kobj) reference is never dropped.
It looks like this could happen if two processes want to unregister the
same kobject at the same time.

Shouldn't sysfs_break_active_protection() do this?

kobject_get(kobj);
kn = kernfs_find_and_get(kobj->sd, attr->name);
if (kn)
kernfs_break_active_protection(kn);
+ else
+ kobject_put(kobj);
return kn;

Alan Stern

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