On Mon 21-09-20 16:43:55, Christian Brauner wrote: > On Mon, Sep 21, 2020 at 10:38:47AM -0400, Tejun Heo wrote: > > Hello, > > > > On Mon, Sep 21, 2020 at 04:28:34PM +0200, Michal Hocko wrote: > > > Fundamentaly CLONE_INTO_CGROUP is similar to regular fork + move to the > > > target cgroup after the child gets executed. So in principle there > > > shouldn't be any big difference. Except that the move has to be explicit > > > and the the child has to have enough privileges to move itself. I am not > > > > Yeap, they're supposed to be the same operations. We've never clearly > > defined how the accounting gets split across moves because 1. it's > > inherently blurry and difficult 2. doesn't make any practical difference for > > the recommended and vast majority usage pattern which uses migration to seed > > the new cgroup. CLONE_INTO_CGROUP doesn't change any of that. > > > > > completely sure about CLONE_INTO_CGROUP model though. According to man > > > clone(2) it seems that O_RDONLY for the target cgroup directory is > > > sufficient. That seems much more relaxed IIUC and it would allow to fork > > > into a different cgroup while keeping a lot of resources in the parent's > > > proper. > > > > If the man page is documenting that, it's wrong. cgroup_css_set_fork() has > > an explicit cgroup_may_write() test on the destination cgroup. > > CLONE_INTO_CGROUP should follow exactly the same rules as regular > > migrations. > > Indeed! > The O_RDONLY mention on the manpage doesn't make sense but it is > explained that the semantics are exactly the same for moving via the > filesystem: OK, if the semantic is the same as for the task migration then I do not see any (new) problems. Care to point me where the actual check is enforced? For the migration you need a write access to cgroup.procs but if the API expects directory fd then I am not sure how that would expose the same behavior. -- Michal Hocko SUSE Labs
