On 2013/8/29 5:03, Tejun Heo wrote:
> ae7f164a09 ("cgroup: move cgroup->subsys[] assignment to
> online_css()") moved cgroup->subsys[] assignements later in
> cgroup_create() but didn't update error handling path accordingly
> leaking later css's after an online_css() failure.
>
> This patch moves reference bumping inside online_css() loop, clears
> css_ar[] as css's are brought online successfully, and updates
> err_destroy path so that either a css is fully online and destroyed by
> cgroup_destroy_locked() or the error path frees it. This creates a
> duplicate css free logic in the error path but it will be cleaned up
> soon.
>
> Signed-off-by: Tejun Heo <[email protected]>
> ---
> kernel/cgroup.c | 23 +++++++++++++++--------
> 1 file changed, 15 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index b5f4989..a4168cf 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -4489,14 +4489,6 @@ static long cgroup_create(struct cgroup *parent,
> struct dentry *dentry,
> list_add_tail_rcu(&cgrp->sibling, &cgrp->parent->children);
> root->number_of_cgroups++;
>
> - /* each css holds a ref to the cgroup's dentry and the parent css */
> - for_each_root_subsys(root, ss) {
> - struct cgroup_subsys_state *css = css_ar[ss->subsys_id];
> -
> - dget(dentry);
> - css_get(css->parent);
> - }
> -
> /* hold a ref to the parent's dentry */
> dget(parent->dentry);
>
> @@ -4508,6 +4500,13 @@ static long cgroup_create(struct cgroup *parent,
> struct dentry *dentry,
> if (err)
> goto err_destroy;
If online_css() returns -error, it means cgroup->subsys[ss->subsys_id] == NULL,
>
> + /* each css holds a ref to the cgroup's dentry and parent css */
> + dget(dentry);
> + css_get(css->parent);
> +
> + /* mark it consumed for error path */
> + css_ar[ss->subsys_id] = NULL;
> +
> if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
> parent->parent) {
> pr_warning("cgroup: %s (%d) created nested cgroup for
> controller \"%s\" which has incomplete hierarchy support. Nested cgroups may
> change behavior in the future.\n",
> @@ -4554,6 +4553,14 @@ err_free_cgrp:
> return err;
>
> err_destroy:
> + for_each_root_subsys(root, ss) {
> + struct cgroup_subsys_state *css = css_ar[ss->subsys_id];
> +
> + if (css) {
> + percpu_ref_cancel_init(&css->refcnt);
> + ss->css_free(css);
> + }
> + }
> cgroup_destroy_locked(cgrp);
Now cgroup_destroy_locked() is called:
for_each_root_subsys(cgrp->root, ss)
kill_css(cgroup_css(cgrp, ss));
cgroup_css(cgrp, ss) will return NULL and pass it to kill_css(), which leads
to NULL pointer deref ?
> mutex_unlock(&cgroup_mutex);
> mutex_unlock(&dentry->d_inode->i_mutex);
>
(I'll go through the patchset tomorrow.)
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