On Wed, Oct 05, 2022 at 06:47:31AM -1000, Tejun Heo <tj@xxxxxxxxxx> wrote: > Hmm... isn't current's root cgrp guaranteed to be alive? True on the default hierarchy. v1 hierarchies (singular ones with root cgroup only) can be unmounted. > How would cgroup_get_live() fail? kill_sb is not synchronized via css_set_lock. > Also, shouldn't cgroup_get() enough for path walking? If ref count dropped to zero, release callback (css_release_work_fn) would be queued, cgroup_get would increase the refcount but it won't cancel this. Note these were concerns with the first version of the patch that also touched cgroup_show_path() (that processes v1 hierarchies too). With the reduction I avoided this. Strictly speaking, even css_set_lock is unnecessary around current_cgns_cgroup_from_root() when called with cgrp_dfl_root as the cset->cgrp_links is not traversed at all. > If you really wanna do it this way, can you please add a detailed comment > here why this is safe? But I'd prefer just doing a strightforward ref > inc/dec around it. I see the the extraction under css_set_lock without inc/dec turns out confusing. Let me expand the idea above and avoid css_set_lock completely (another message). Michal
