Quoting Daniel P. Berrange (berrange@xxxxxxxxxx): > On Fri, Jun 28, 2013 at 02:01:55PM -0400, Vivek Goyal wrote: > > On Fri, Jun 28, 2013 at 05:05:13PM +0200, Michal Hocko wrote: > > > On Thu 27-06-13 22:01:38, Tejun Heo wrote: > > > > Hello, Mike. > > > > > > > > On Fri, Jun 28, 2013 at 06:49:10AM +0200, Mike Galbraith wrote: > > > > > I always thought that was a very cool feature, mkdir+echo, poof done. > > > > > Now maybe that interface is suboptimal for serious usage, but it makes > > > > > the things usable via dirt simple scripts, very flexible, nice. > > > > > > > > Oh, that in itself is not bad. I mean, if you're root, it's pretty > > > > easy to play with and that part is fine. But combined with the > > > > hierarchical nature of cgroup and file permissions, it encourages > > > > people to "deligate" subdirectories to less previledged domains, > > > > > > OK, this really depends on what you expose to non-root users. I have > > > seen use cases where admin prepares top-level which is root-only but > > > it allows creating sub-groups which are under _full_ control of the > > > subdomain. This worked nicely for memcg for example because hard limit, > > > oom handling and other knobs are hierarchical so the subdomain cannot > > > overwrite what admin has said. > > > > > > > which > > > > in turn leads to normal binaries to manipulate them directly, which is > > > > where the horror begins. We end up exposing control knobs which are > > > > tightly coupled to kernel implementation details right into lay > > > > binaries and scripts directly used by end users. > > > > > > > > I think this is the first time this happened, which is probably why > > > > nobody really noticed the mess earlier. > > > > > > > > Anyways, if you're root, you can keep doing whatever you want. > > > > > > OK, so libcgroup's rules daemon will still work and place my tasks in > > > appropriate cgroups? > > > > Do you use that daemon in practice? For user session logins, I think > > systemd has plans to put user sessions in a cgroup (kind of making > > pam_cgroup redundant). > > > > Other functionality rulesengined was providing moving tasks automatically > > in a cgroup based on executable name. I think that was racy and not > > many people had liked it. > > Regardless of the changes being proposed, IMHO, the cgrulesd should > never be used. It is just outright dangerous for a daemon to be > arbitrarily re-arranging what cgroups a process is placed in without > the applications being aware of it. It can only be safely used in a > scenario where cgroups are exclusively used by the administrator, > and never used by applications for their own needs. Even then it's not safe, since if the program quickly forks or clones a few times, you can end up with some of the tasks being reclassified and some not. > > IIUC, systemd can't disable access to cgroupfs from other utilities. > > The kernel can exposed a knob that would allow systemd to lock that > down Gah - why would you give him that idea? :) But yes, I'd sort of assume that was coming, eventually. -serge _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
