On Wed 2021-12-15 16:35:24, Greg Kroah-Hartman wrote: > On Wed, Dec 15, 2021 at 09:19:59AM +0100, Petr Mladek wrote: > > On Tue 2021-12-14 16:50:15, Greg Kroah-Hartman wrote: > > > > > > kobject_init() does allocate things internally, where does it say it > > > does not? What is trying to be "fixed" here? > > > > Could you please show where things are allocated in kobject_init()? > > I do not see it in the code! > > > > It looks to me like a cargo cult claim to me. > > Hm, I thought I saw it yesterday when I reviewed the code. Let me look > again... > > > Documentation/core-api/kobject.rst says: > > > > Once you registered your kobject via kobject_add(), you must never use > > kfree() to free it directly. The only safe way is to use kobject_put(). > > > > kobject_add() makes perfect sense because it copies the name, takes > > reference to the parent, etc. > > > > kobject_init() just initializes the structure members and nothing else. > > Now it does. In the past, I think we did create some memory. I know > when we hook debugobjects up to kobjects (there's an external patch for > that floating around somewhere), that is one reason to keep the > kobject_put() rule, and there might have been other reasons in the past > 20+ years as well. > > So yes, while you are correct today, the "normal" reference counted > object model patern is "after the object is initialized, it MUST only be > freed by handling its reference count." So let's stick to that rule for > now. Good point. > If you want, I can put some code in the kobject_init() logic to force > this to be the case if it bothers you :) I actually know about one case where this might be very useful. There is the problem with kobject lifetime and module removal. module is removed after mod->exit() callback finishes. But some kobject release() callbacks might be delayed, especillay when CONFIG_DEBUG_KOBJECT_RELEASE is enabled. I have proposed there a solution where kobject_add_internal() takes reference on the module. It would make sure that the module will stay in the memory until the release callbacks is called, see https://lore.kernel.org/all/Ya84O2%2FnYCyNb%2Ffp@alley/ But kobject_add_internal() is not the right place. The reference on the module should be taken already in kobject_init() because the release callbacks might be used after this point. Best Regards, Petr
