On Mon, May 20, 2019 at 10:41:26AM +0200, Pavel Hrdina wrote: > On Sat, May 18, 2019 at 12:56:12AM +0000, Roman Gushchin wrote: > > On Fri, May 17, 2019 at 12:12:51PM +0200, Pavel Hrdina wrote: > > > On Thu, May 16, 2019 at 10:25:50AM -0700, Alexei Starovoitov wrote: > > > > On Thu, May 16, 2019 at 10:15 AM Roman Gushchin <guro@xxxxxx> wrote: > > > > > > > > > > On Thu, May 16, 2019 at 05:31:44PM +0200, Pavel Hrdina wrote: > > > > > > On Thu, May 16, 2019 at 03:22:33PM +0000, Roman Gushchin wrote: > > > > > > > On Thu, May 16, 2019 at 12:39:15PM +0200, Jiri Olsa wrote: > > > > > > > > hi, > > > > > > > > Pavel reported an issue with bpf programs (attached to cgroup) > > > > > > > > not being released at the time when the cgroup is removed and > > > > > > > > are still visible in 'bpftool prog' list afterwards. > > > > > > > > > > > > > > Hi Jiri! > > > > > > > > > > > > > > Can you, please, try the patch from > > > > > > > https://github.com/rgushchin/linux/commit/f77afa1952d81a1afa6c4872d342bf6721e148e2 ? > > > > > > > > > > > > > > It should solve the problem, and I'm about to post it upstream. > > > > > > > > > > > > Perfect, I'll give it a try with full libvirt setup as well. > > > > > > > > > > > > Can we have this somehow detectable from user-space so libvirt can > > > > > > decide when to use BPF or not? I would like to avoid using BPF with > > > > > > libvirt if this issue is not fixed and we cannot simply workaround it > > > > > > as systemd automatically removes cgroups for us. > > > > > > > > > > Hm, I don't think there is a good way to detect it from userspace. > > > > > At least I have no good ideas. Alexei? Daniel? > > > > > > > > > > If you're interested in a particular stable version, we can probably > > > > > treat it as a "fix", and backport. > > > > > > > > right. > > > > also user space workaround is trivial. > > > > Just detach before rmdir. > > > > > > Well yes, it's trivial but not if you are using machined from systemd. > > > Once libvirt kills QEMU process systemd automatically removes the > > > cgroup so we don't have any chance to remove the BPF program. > > > > > > Would it be too ugly to put something into > > > '/sys/kernel/cgroup/features'? > > > > I thought about it, but it seems that /sys/kernel/cgroup/features is also > > relatively new. So if we're not going to backport it (I mean auto-detaching), > > than we can simple look at the kernel version, right? > > If you think only about upstream then the version check is in most cases > good enough, but usually that's not the case and patches are backported > to downstream distributions as well. > > Yes, that file was introduced in kernel 4.15 so there are some > limitations where the fix would be introspectable. > > > If we're going to backport it, the question is which stable version we're > > looking at. > > > > In general, I don't see any reasons why cgroup/features can't be used. > > Perfect, in that case I would prefer if we could export it in > cgroup/features as it will be easier for user-space to figure out > whether it's safe to relay on proper cleanup behavior or not and > it will make downstream distributions life easier. Hello, Pavel! Tejun noticed that cgroup features are supposed to match cgroupfs mount options, so it can't be used here. And this >= 4.15 limitation is also a significant constraint. Thanks!
