On Tue, Oct 19, 2021 at 08:23:51AM +0200, Miroslav Benes wrote: > > > By you only addressing the deadlock as a requirement on approach a) you are > > > forgetting that there *may* already be present drivers which *do* implement > > > such patterns in the kernel. I worked on addressing the deadlock because > > > I was informed livepatching *did* have that issue as well and so very > > > likely a generic solution to the deadlock could be beneficial to other > > > random drivers. > > > > In-tree zram doesn't have such deadlock, if livepatching has such AA deadlock, > > just fixed it, and seems it has been fixed by 3ec24776bfd0. > > I would not call it a fix. It is a kind of ugly workaround because the > generic infrastructure lacked (lacks) the proper support in my opinion. > Luis is trying to fix that. What is the proper support of the generic infrastructure? I am not familiar with livepatching's model(especially with module unload), you mean livepatching have to do the following way from sysfs: 1) during module exit: mutex_lock(lp_lock); kobject_put(lp_kobj); mutex_unlock(lp_lock); 2) show()/store() method of attributes of lp_kobj mutex_lock(lp_lock) ... mutex_unlock(lp_lock) IMO, the above usage simply caused AA deadlock. Even in Luis's patch 'zram: fix crashes with cpu hotplug multistate', new/same AA deadlock (hot_remove_store() vs. disksize_store() or reset_store()) is added because hot_remove_store() isn't called from module_exit(). Luis tries to delay unloading module until all show()/store() are done. But that can be obtained by the following way simply during module_exit(): kobject_del(lp_kobj); //all pending store()/show() from lp_kobj are done, //no new store()/show() can come after //kobject_del() returns mutex_lock(lp_lock); kobject_put(lp_kobj); mutex_unlock(lp_lock); Or can you explain your requirement on kobject/module unload in a bit details? Thanks, Ming
