On Tue 2021-10-26 23:37:30, Ming Lei wrote: > On Tue, Oct 26, 2021 at 10:48:18AM +0200, Petr Mladek wrote: > > Below are more details about the livepatch code. I hope that it will > > help you to see if zram has similar problems or not. > > > > We have kobject in three structures: klp_func, klp_object, and > > klp_patch, see include/linux/livepatch.h. > > > > These structures have to be statically defined in the module sources > > because they define what is livepatched, see > > samples/livepatch/livepatch-sample.c > > > > The kobject is used there to show information about the patch, patched > > objects, and patched functions, in sysfs. And most importantly, > > the sysfs interface can be used to disable the livepatch. > > > > The problem with static structures is that the module must stay > > in the memory as long as the sysfs interface exists. It can be > > solved in module_exit() callback. It could wait until the sysfs > > interface is destroyed. > > > > kobject API does not support this scenario. The relase() callbacks > > kobject_delete() is for supporting this scenario, that is why we don't > need to grab module refcnt before calling show()/store() of the > kobject's attributes. > > kobject_delete() can be called in module_exit(), then any show()/store() > will be done after kobject_delete() returns. I am a bit confused. I do not see kobject_delete() anywhere in kernel sources. I see only kobject_del() and kobject_put(). AFAIK, they do _not_ guarantee that either the sysfs interface was destroyed or the release callbacks were called. For example, see schedule_delayed_work(&kobj->release, delay) in kobject_release(). By other words, anyone could still be using either the sysfs interface or the related structures after kobject_del() or kobject_put() returns. IMHO, kobject API does not support static structures and module removal. Best Regards, Petr
