On 6/24/2022 6:35 PM, Jason Gunthorpe wrote:
On Fri, Jun 24, 2022 at 06:23:48PM +0530, Kirti Wankhede wrote:
On 6/24/2022 6:03 PM, Jason Gunthorpe wrote:
On Fri, Jun 24, 2022 at 05:59:58PM +0530, Kirti Wankhede wrote:
The reason this is here is because the type->parent is used in a few
places and is put back in release:
@@ -81,7 +81,7 @@ static void mdev_type_release(struct kobject *kobj)
pr_debug("Releasing group %s\n", kobj->name);
/* Pairs with the get in add_mdev_supported_type() */
- mdev_put_parent(type->parent);
+ put_device(type->parent->dev);
kfree(type);
}
If this was a simple sysfs kobj with only a show/store we wouldn't
need to do anything as the natural kobj parentage holds a ref up to
the struct device - but this kobj is used internally, ie dependent
from mdev_device_create(), independently of the normal sysfs
life-cycle so that doesn't protect enough either.
Life span of 'type' is from mdev_register_device to mdev_unregister_device.
If device/parent is being unregistered then only types are removed, so
referencing 'type' from mdev_device_create() is still safe. Therefore,
parent device's reference should be held and release from
register-unregister call.
No, I've already explained this.
Its not correct.
kobject_init_and_add(&type->kobj, ...) which called from
mdev_register_parent()
-> parent_create_sysfs_files() holds reference for type->kobj
-> add_mdev_supported_type_groups()
-> add_mdev_supported_type()
-> kobject_init_and_add(&type->kobj)
This is released from
mdev_unregister_parent()
-> parent_remove_sysfs_files()
-> kset_unregister()
It is not kset_unregister() that puts back.
-> remove_mdev_supported_type()
-> kobject_put(&type->kobj) // pairs with kobject_init_and_add
that's correct, my bad.
So what is the issue? This is a properly paired usage of the ref.
In the next patch [3/13] of this series, these calltraces are changed as
mdev_register_parent()
-> mdev_type_add()
-> kobject_init_and_add(&type->kobj, ...) holds reference for
type->kobj
which is released from
mdev_unregister_parent()
-> mdev_type_remove()
-> kobject_put(&type->kobj)
This is the same logic? What is the problem?
Pasting here your comment:
>>>>> the struct device - but this kobj is used internally, ie dependent
>>>>> from mdev_device_create(), independently of the normal sysfs
>>>>> life-cycle so that doesn't protect enough either.
Since there references are held, its safe.
Thanks,
Kirti
