On Tue, Nov 02, 2021 at 03:15:15PM +0100, Petr Mladek wrote: > 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(). After kobject_del() returns, no one can call run into show()/store(), and all pending show()/store() are drained meantime. But yes, the release handler may still be called later, and the kobject has to be freed during or before module_exit(). https://lore.kernel.org/lkml/20211101112548.3364086-2-ming.lei@xxxxxxxxxx/ > > By other words, anyone could still be using either the sysfs interface > or the related structures after kobject_del() or kobject_put() > returns. No, no one can do that after kobject_del() returns. > > IMHO, kobject API does not support static structures and module > removal. But so far klp_patch can only be defined as static instance, and it depends on the implementation, especially the release handler. Thanks, Ming
