On Tue, May 10, 2022 at 11:34 AM Tejun Heo <tj@xxxxxxxxxx> wrote:
>
> On Tue, May 10, 2022 at 12:18:04AM +0000, Yosry Ahmed wrote:
> > The current implementation of cgroup_get_from_id() only searches the
> > default hierarchy for the given id. Make it compatible with cgroup v1 by
> > looking through all the roots instead.
> >
> > cgrp_dfl_root should be the first element in the list so there shouldn't
> > be a performance impact for cgroup v2 users (in the case of a valid id).
> >
> > Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
> > ---
> > kernel/cgroup/cgroup.c | 10 ++++++++--
> > 1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> > index af703cfcb9d2..12700cd21973 100644
> > --- a/kernel/cgroup/cgroup.c
> > +++ b/kernel/cgroup/cgroup.c
> > @@ -5970,10 +5970,16 @@ void cgroup_path_from_kernfs_id(u64 id, char *buf, size_t buflen)
> > */
> > struct cgroup *cgroup_get_from_id(u64 id)
> > {
> > - struct kernfs_node *kn;
> > + struct kernfs_node *kn = NULL;
> > struct cgroup *cgrp = NULL;
> > + struct cgroup_root *root;
> > +
> > + for_each_root(root) {
> > + kn = kernfs_find_and_get_node_by_id(root->kf_root, id);
> > + if (kn)
> > + break;
> > + }
>
> I can't see how this can work. You're smashing together separate namespaces
> and the same IDs can exist across multiple of these hierarchies. You'd need
> a bigger surgery to make this work for cgroup1 which would prolly involve
> complications around 32bit ino's and file handle support too, which I'm not
> likely to ack, so please give it up on adding these things to cgroup1.
>
> Nacked-by: Tejun Heo <tj@xxxxxxxxxx>
>
> Thanks.
Completely understandable. I sent this patch knowing that it likely
will not be accepted, with hopes of hearing feedback on whether this
can be done in a simple way or not. Looks like I got my answer, so
thanks for the info!
Will drop this patch in the incoming versions.
>
> --
> tejun
