On Thu, Aug 01, 2024 at 10:01:20AM GMT, Oleg Nesterov wrote: > OK, I won't argue, but .... > > On 08/01, Christian Brauner wrote: > > > > On Wed, Jul 31, 2024 at 04:51:33PM GMT, Oleg Nesterov wrote: > > > On 07/31, Christian Brauner wrote: > > > > > > > > It's currently possible to create pidfds for kthreads but it is unclear > > > > what that is supposed to mean. Until we have use-cases for it and we > > > > figured out what behavior we want block the creation of pidfds for > > > > kthreads. > > > > > > Hmm... could you explain your concerns? Why do you think we should disallow > > > pidfd_open(pid-of-kthread) ? > > > > It basically just works now and it's not intentional - at least not on > > my part. You can't send signals to them, > > Yes, you can't send signals to kthread. So what? > > You can't send signals to the normal processes if check_kill_permission() > fails. And even if you are root, you can't send an unhandled signal via > pidfd = pidfd_open(1). > > > you may or may not get notified > > via poll when a kthread exits. > > Why? the exiting kthread should not differ in this respect? Why do you want to allow it? I see zero reason to get a reference to a kthread if there's no use-case for it. kthreads are mostly a kernel thing so why give userspace handles to it. And as I said before, there's userspace out there that's already confused why they can get references to them in the first place. > > > (So imho this causes more confusion then it is actually helpful. If we > > add supports for kthreads I'd also like pidfs to gain a way to identify > > them via statx() or fdinfo.) > > /proc/$pid/status has a "Kthread" field... Going forward, I don't want to force people to parse basic stuff out of procfs. Ideally, they'll be able to mostly rely on pidfd operations only.
