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SubjectRe: [PATCH 2/4] cgroup:add css_is_populated
Li-san, If you don't like this, could you give me an idea for
"How to check cgroup is fully ready or not" ?

BTW, why "we have a half filled direcotory - oh well" is allowed....
Thanks,
-Kame



On Thu, 15 Jan 2009 19:27:12 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>
> cgroup creation is done in several stages.
> After allocated and linked to cgroup's hierarchy tree, all necessary
> control files are created.
>
> When using CSS_ID, scanning cgroups without cgrouo_lock(), status
> of cgroup is important. At removal of cgroup/css, css_tryget() works fine
> and we can write a safe code. At creation, we need some flag to show
> "This cgroup is not ready yet"
>
> This patch adds CSS_POPULATED flag.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>
> ---
> Index: mmotm-2.6.29-Jan14/include/linux/cgroup.h
> ===================================================================
> --- mmotm-2.6.29-Jan14.orig/include/linux/cgroup.h
> +++ mmotm-2.6.29-Jan14/include/linux/cgroup.h
> @@ -69,6 +69,7 @@ struct cgroup_subsys_state {
> enum {
> CSS_ROOT, /* This CSS is the root of the subsystem */
> CSS_REMOVED, /* This CSS is dead */
> + CSS_POPULATED, /* This CSS finished all initialization */
> };
>
> /*
> @@ -90,6 +91,11 @@ static inline bool css_is_removed(struct
> return test_bit(CSS_REMOVED, &css->flags);
> }
>
> +static inline bool css_is_populated(struct cgroup_subsys_state *css)
> +{
> + return test_bit(CSS_POPULATED, &css->flags);
> +}
> +
> /*
> * Call css_tryget() to take a reference on a css if your existing
> * (known-valid) reference isn't already ref-counted. Returns false if
> Index: mmotm-2.6.29-Jan14/kernel/cgroup.c
> ===================================================================
> --- mmotm-2.6.29-Jan14.orig/kernel/cgroup.c
> +++ mmotm-2.6.29-Jan14/kernel/cgroup.c
> @@ -2326,8 +2326,10 @@ static int cgroup_populate_dir(struct cg
> }
>
> for_each_subsys(cgrp->root, ss) {
> + struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
> if (ss->populate && (err = ss->populate(ss, cgrp)) < 0)
> return err;
> + set_bit(CSS_POPULATED, &css->flags);
> }
>
> return 0;
>
> --
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