On Wed, Dec 13, 2017 at 04:13:07PM +0900, Byungchul Park wrote: > > Therefore, I want to say the fundamental problem > comes from classification, not cross-release > specific. You keep saying that it is "just" a matter of classificaion. However, it is not obvious how to do the classification in a sane manner. And this is why I keep pointing out that there is no documentation on how to do this, and somehow you never respond to this point.... In the case where you have multiple unrelated subsystems that can be stacked in different ways, with potentially multiple instances stacked on top of each other, it is not at all clear to me how this problem should be solved. It was said on one of these threads (perhaps by you, perhaps by someone else), that we can't expect the lockdep maintainers to understand all of the subsystems in the kernels, and so therefore it must be up to the subsystem maintainers to classify the locks. I interpreted this as the lockdep maintainers saying, "hey, not my fault, it's the subsystem maintainer's fault for not properly classifying the locks" --- and thus dumping the responsibility in the subsystem maintainers' laps. I don't know if the situation is just that lockdep is insufficiently documented, and with the proper tutorial, it would be obvious how to solve the classification problem. Or, if perhaps, there *is* no way to solve the classification problem, at least not in a general form. For example --- suppose we have a network block device on which there is an btrfs file system, which is then exported via NFS. Now all of the TCP locks will be used twice for two different instances, once for the TCP connection for the network block device, and then for the NFS export. How exactly are we supposed to classify the locks to make it all work? Or the loop device built on top of an ext4 file system which on a LVM/device mapper device. And suppose the loop device is then layered with a dm-error device for regression testing, and with another ext4 file system on top of that? How exactly are we supposed to classify the locks in that situation? Where's the documentation and tutorials which explain how to make this work, if the responsibility is going to be dumped on the subsystem maintainers' laps? Or if the lockdep maintainers are expected to fix and classify all of these locks, are you volunteering to do this? How hard is it exactly to do all of this classification work, no matter whose responsibility it will ultimately be? And if the answer is that it is too hard, then let me gently suggest to you that perhaps, if this is a case, that maybe this is a fundamental and fatal flaw with the cross-release and completion lockdep feature? Best regards, - Ted
