Hi Michal & Roman,
Thank you for your review.
On 10/12/21 12:21 AM, Michal Koutný wrote:
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?
Before this commit, percpu_ref is embedded in cgroup, it can be freed
along with cgroup, so there is no memory leak. Since this commit, it
causes the memory leak.
Should I change it to "Fixes: 4bfc0bb2c60e ("bpf: decouple the lifetime
of cgroup_bpf from cgroup itself")"?
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 :-)
Thanks for pointing it out. I will send a V2 to fix this.
Thanks,
Quanyang
percpu_ref_kill(&root->cgrp.self.refcnt);
+ }
cgroup_put(&root->cgrp);
kernfs_kill_sb(sb);
}
