On Wed 28-08-19 19:56:58, Tetsuo Handa wrote: > On 2019/08/28 19:32, Michal Hocko wrote: > >> Speak of my cases, those who take care of their systems are not developers. > >> And they afraid changing code that runs in kernel mode. They unlikely give > >> permission to install SystemTap/eBPF scripts. As a result, in many cases, > >> the root cause cannot be identified. > > > > Which is something I would call a process problem more than a kernel > > one. Really if you need to debug a problem you really have to trust > > those who can debug that for you. We are not going to take tons of code > > to the kernel just because somebody is afraid to run a diagnostic. > > > > This is a problem of kernel development process. I disagree. Expecting that any larger project can be filled with the (close to) _full_ and ready to use introspection built in is just insane. We are trying to help with a generally useful information but you simply cannot cover most existing failure paths. > >> Moreover, we are talking about OOM situations, where we can't expect userspace > >> processes to work properly. We need to dump information we want, without > >> counting on userspace processes, before sending SIGKILL. > > > > Yes, this is an inherent assumption I was making and that means that > > whatever dynamic hooks would have to be registered in advance. > > > > No. I'm saying that neither static hooks nor dynamic hooks can work as > expected if they count on userspace processes. Registering in advance is > irrelevant. Whether it can work without userspace processes is relevant. I am not saying otherwise. I do not expect any userspace process to dump any information or read it from elswhere than from the kernel log. > Also, out-of-tree codes tend to become defunctional. We are trying to debug > problems caused by in-tree code. Breaking out-of-tree debugging code just > because in-tree code developers don't want to pay the burden of maintaining > code for debugging problems caused by in-tree code is a very bad idea. This is a simple math of cost/benefit. The maintenance cost is not free and paying it for odd cases most people do not care about is simply not sustainable, we simply do not have that much of a man power. -- Michal Hocko SUSE Labs
