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cgroup: move cgroup->subsys[] assignment to online_css()

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Currently, css (cgroup_subsys_state) lifetime is tied to that of the
associated cgroup.  With the planned unified hierarchy, css's will be
dynamically created and destroyed within the lifetime of a cgroup.  To
enable such usages, css's will be individually RCU protected instead
of being tied to the cgroup.

In preparation, this patch moves cgroup->subsys[] assignment from
init_css() to online_css().  As this means that a newly initialized
css should be remembered separately and that cgroup_css() returns NULL
between init and online, cgroup_create() is updated so that it stores
newly created css's in a local array css_ar[] and
cgroup_init/load_subsys() are updated to use local variable @css
instead of using cgroup_css().  This change also slightly simplifies
error path of cgroup_create().

While this patch changes when cgroup->subsys[] is initialized, this
change isn't visible to subsystems or userland.

v2: This patch wasn't updated accordingly after the previous "cgroup:
    reorganize css init / exit paths" was updated leading to missing a
    css_ar[] conversion in cgroup_create() and thus boot failure.  Fix
    it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
This commit is contained in:
Tejun Heo 2013-08-13 20:22:50 -04:00
commit ae7f164a09
1 changed files with 11 additions and 10 deletions
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21
kernel/cgroup.c
View file

@ -4321,7 +4321,6 @@ static void init_css(struct cgroup_subsys_state *css, struct cgroup_subsys *ss,
css->flags |= CSS_ROOT; css->flags |= CSS_ROOT;
BUG_ON(cgroup_css(cgrp, ss->subsys_id)); BUG_ON(cgroup_css(cgrp, ss->subsys_id));
rcu_assign_pointer(cgrp->subsys[ss->subsys_id], css);
} }
/* invoke ->css_online() on a new CSS and mark it online if successful */ /* invoke ->css_online() on a new CSS and mark it online if successful */
@ -4334,8 +4333,10 @@ static int online_css(struct cgroup_subsys_state *css)
if (ss->css_online) if (ss->css_online)
ret = ss->css_online(css); ret = ss->css_online(css);
if (!ret) if (!ret) {
css->flags |= CSS_ONLINE; css->flags |= CSS_ONLINE;
rcu_assign_pointer(css->cgroup->subsys[ss->subsys_id], css);
}
return ret; return ret;
} }
@ -4366,6 +4367,7 @@ static void offline_css(struct cgroup_subsys_state *css)
static long cgroup_create(struct cgroup *parent, struct dentry *dentry, static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
umode_t mode) umode_t mode)
{ {
struct cgroup_subsys_state *css_ar[CGROUP_SUBSYS_COUNT] = { };
struct cgroup *cgrp; struct cgroup *cgrp;
struct cgroup_name *name; struct cgroup_name *name;
struct cgroupfs_root *root = parent->root; struct cgroupfs_root *root = parent->root;
@ -4433,12 +4435,11 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
err = PTR_ERR(css); err = PTR_ERR(css);
goto err_free_all; goto err_free_all;
} }
css_ar[ss->subsys_id] = css;
err = percpu_ref_init(&css->refcnt, css_release); err = percpu_ref_init(&css->refcnt, css_release);
if (err) { if (err)
ss->css_free(css);
goto err_free_all; goto err_free_all;
}
init_css(css, ss, cgrp); init_css(css, ss, cgrp);
@ -4467,7 +4468,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
/* each css holds a ref to the cgroup's dentry and the parent css */ /* each css holds a ref to the cgroup's dentry and the parent css */
for_each_root_subsys(root, ss) { for_each_root_subsys(root, ss) {
struct cgroup_subsys_state *css = cgroup_css(cgrp, ss->subsys_id); struct cgroup_subsys_state *css = css_ar[ss->subsys_id];
dget(dentry); dget(dentry);
percpu_ref_get(&css->parent->refcnt); percpu_ref_get(&css->parent->refcnt);
@ -4478,7 +4479,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
/* creation succeeded, notify subsystems */ /* creation succeeded, notify subsystems */
for_each_root_subsys(root, ss) { for_each_root_subsys(root, ss) {
struct cgroup_subsys_state *css = cgroup_css(cgrp, ss->subsys_id); struct cgroup_subsys_state *css = css_ar[ss->subsys_id];
err = online_css(css); err = online_css(css);
if (err) if (err)
@ -4511,7 +4512,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
err_free_all: err_free_all:
for_each_root_subsys(root, ss) { for_each_root_subsys(root, ss) {
struct cgroup_subsys_state *css = cgroup_css(cgrp, ss->subsys_id); struct cgroup_subsys_state *css = css_ar[ss->subsys_id];
if (css) { if (css) {
percpu_ref_cancel_init(&css->refcnt); percpu_ref_cancel_init(&css->refcnt);
@ -4793,7 +4794,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
* need to invoke fork callbacks here. */ * need to invoke fork callbacks here. */
BUG_ON(!list_empty(&init_task.tasks)); BUG_ON(!list_empty(&init_task.tasks));
BUG_ON(online_css(cgroup_css(cgroup_dummy_top, ss->subsys_id))); BUG_ON(online_css(css));
mutex_unlock(&cgroup_mutex); mutex_unlock(&cgroup_mutex);
@ -4897,7 +4898,7 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
} }
write_unlock(&css_set_lock); write_unlock(&css_set_lock);
ret = online_css(cgroup_css(cgroup_dummy_top, ss->subsys_id)); ret = online_css(css);
if (ret) if (ret)
goto err_unload; goto err_unload;