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Message-ID: <52084CC5.8050207@huawei.com>
Date: Mon, 12 Aug 2013 10:47:33 +0800
From: Li Zefan <lizefan@...wei.com>
To: Tejun Heo <tj@...nel.org>
CC: <containers@...ts.linux-foundation.org>, <cgroups@...r.kernel.org>,
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 07/14] cgroup: reorganize css init / exit paths
> /* invoke ->css_online() on a new CSS and mark it online if successful */
> -static int online_css(struct cgroup_subsys *ss, struct cgroup *cgrp)
> +static int online_css(struct cgroup_subsys_state *css)
> {
> - struct cgroup_subsys_state *css = cgroup_css(cgrp, ss->subsys_id);
> + struct cgroup_subsys *ss = css->ss;
> int ret = 0;
>
> lockdep_assert_held(&cgroup_mutex);
> @@ -4342,9 +4340,9 @@ static int online_css(struct cgroup_subsys *ss, struct cgroup *cgrp)
> }
>
> /* if the CSS is online, invoke ->css_offline() on it and mark it offline */
> -static void offline_css(struct cgroup_subsys *ss, struct cgroup *cgrp)
> +static void offline_css(struct cgroup_subsys_state *css)
> {
> - struct cgroup_subsys_state *css = cgroup_css(cgrp, ss->subsys_id);
> + struct cgroup_subsys *ss = css->ss;
>
> lockdep_assert_held(&cgroup_mutex);
>
> @@ -4442,10 +4440,10 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
> goto err_free_all;
> }
>
> - init_cgroup_css(css, ss, cgrp);
> + init_css(css, ss, cgrp);
>
> if (ss->use_id) {
> - err = alloc_css_id(ss, parent, cgrp);
> + err = alloc_css_id(css);
> if (err)
> goto err_free_all;
> }
> @@ -4467,20 +4465,18 @@ 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 */
> + /* hold a ref to the parent's dentry */
> + dget(parent->dentry);
> +
> for_each_root_subsys(root, ss) {
> struct cgroup_subsys_state *css = cgroup_css(cgrp, ss->subsys_id);
>
> + /* each css holds a ref to the cgroup and the parent css */
> dget(dentry);
> percpu_ref_get(&css->parent->refcnt);
We called dget() and percpu_ref_get() for each css unconditionally...
> - }
>
> - /* hold a ref to the parent's dentry */
> - dget(parent->dentry);
> -
> - /* creation succeeded, notify subsystems */
> - for_each_root_subsys(root, ss) {
> - err = online_css(ss, cgrp);
> + /* creation succeeded, notify subsystems */
> + err = online_css(css);
> if (err)
> goto err_destroy;
but now dget() and percpu_ref_get() may not be called for some css's,
but the code in failure path is not updated accordingly, which seems
wrong.
>
> @@ -4700,7 +4696,7 @@ static void cgroup_offline_fn(struct work_struct *work)
> * initate destruction.
> */
> for_each_root_subsys(cgrp->root, ss)
> - offline_css(ss, cgrp);
> + offline_css(cgroup_css(cgrp, ss->subsys_id));
>
> /*
> * Put the css refs from cgroup_destroy_locked(). Each css holds
> @@ -4778,7 +4774,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
> css = ss->css_alloc(cgroup_css(cgroup_dummy_top, ss->subsys_id));
> /* We don't handle early failures gracefully */
> BUG_ON(IS_ERR(css));
> - init_cgroup_css(css, ss, cgroup_dummy_top);
> + init_css(css, ss, cgroup_dummy_top);
>
> /* Update the init_css_set to contain a subsys
> * pointer to this state - since the subsystem is
> @@ -4793,7 +4789,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
> * need to invoke fork callbacks here. */
> BUG_ON(!list_empty(&init_task.tasks));
>
> - BUG_ON(online_css(ss, cgroup_dummy_top));
> + BUG_ON(online_css(cgroup_css(cgroup_dummy_top, ss->subsys_id)));
>
> mutex_unlock(&cgroup_mutex);
>
> @@ -4866,8 +4862,8 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
> ss->root = &cgroup_dummy_root;
>
> /* our new subsystem will be attached to the dummy hierarchy. */
> - init_cgroup_css(css, ss, cgroup_dummy_top);
> - /* init_idr must be after init_cgroup_css because it sets css->id. */
> + init_css(css, ss, cgroup_dummy_top);
> + /* init_idr must be after init_css() because it sets css->id. */
> if (ss->use_id) {
> ret = cgroup_init_idr(ss, css);
> if (ret)
> @@ -4897,7 +4893,7 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
> }
> write_unlock(&css_set_lock);
>
> - ret = online_css(ss, cgroup_dummy_top);
> + ret = online_css(cgroup_css(cgroup_dummy_top, ss->subsys_id));
> if (ret)
> goto err_unload;
>
> @@ -4936,7 +4932,7 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss)
>
> mutex_lock(&cgroup_mutex);
>
> - offline_css(ss, cgroup_dummy_top);
> + offline_css(cgroup_css(cgroup_dummy_top, ss->subsys_id));
>
> if (ss->use_id)
> idr_destroy(&ss->idr);
> @@ -5588,20 +5584,16 @@ static int __init_or_module cgroup_init_idr(struct cgroup_subsys *ss,
> return 0;
> }
>
> -static int alloc_css_id(struct cgroup_subsys *ss, struct cgroup *parent,
> - struct cgroup *child)
> +static int alloc_css_id(struct cgroup_subsys_state *child_css)
> {
> - int subsys_id, i, depth = 0;
> - struct cgroup_subsys_state *parent_css, *child_css;
> + struct cgroup_subsys_state *parent_css = css_parent(child_css);
> struct css_id *child_id, *parent_id;
> + int i, depth;
>
> - subsys_id = ss->subsys_id;
> - parent_css = cgroup_css(parent, subsys_id);
> - child_css = cgroup_css(child, subsys_id);
> parent_id = rcu_dereference_protected(parent_css->id, true);
> depth = parent_id->depth + 1;
>
> - child_id = get_new_cssid(ss, depth);
> + child_id = get_new_cssid(child_css->ss, depth);
> if (IS_ERR(child_id))
> return PTR_ERR(child_id);
>
>
--
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