Re: [PATCH] cgroup: fix memory leak caused by missing cgroup_bpf_offline
From: Michal Koutný <mkoutny@suse.com>
Date: 2021-10-11 16:21:35
Also in:
bpf, cgroups, lkml
Hello. On Thu, Oct 07, 2021 at 08:16:03PM +0800, quanyang.wang@windriver.com 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...
quoted hunk ↗ jump to hunk
+++ 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); }