Hello.
On Thu, Oct 07, 2021 at 08:16:03PM +0800, quanyang.wang@xxxxxxxxxxxxx wrote:
> This is because that root_cgrp->bpf.refcnt.data is allocated by the
> function percpu_ref_init in cgroup_bpf_inherit which is called by
> cgroup_setup_root when mounting, but not freed along with root_cgrp
> when umounting.
Good catch!
> Adding cgroup_bpf_offline which calls percpu_ref_kill to
> cgroup_kill_sb can free root_cgrp->bpf.refcnt.data in umount path.
That is sensible.
> Fixes: 2b0d3d3e4fcfb ("percpu_ref: reduce memory footprint of percpu_ref in fast path")
Why this Fixes:? Is the leak absent before the percpu_ref refactoring?
I guess the embedded data are free'd together with cgroup. Makes me
wonder why struct cgroup_bpf has a separate percpu_ref counter from
struct cgroup...
> +++ b/kernel/cgroup/cgroup.c
> @@ -2147,8 +2147,10 @@ static void cgroup_kill_sb(struct super_block *sb)
> * And don't kill the default root.
> */
> if (list_empty(&root->cgrp.self.children) && root != &cgrp_dfl_root &&
> - !percpu_ref_is_dying(&root->cgrp.self.refcnt))
> + !percpu_ref_is_dying(&root->cgrp.self.refcnt)) {
> + cgroup_bpf_offline(&root->cgrp);
(You made some unnecessary whitespace here breaking indention :-)
> percpu_ref_kill(&root->cgrp.self.refcnt);
> + }
> cgroup_put(&root->cgrp);
> kernfs_kill_sb(sb);
> }
