linux-kernel - Re: [PATCH 2/4] cgroup:add css_is

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Message-Id: <20090116120001.f37e1895.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 16 Jan 2009 12:00:01 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"menage@...gle.com" <menage@...gle.com>,
	"lizf@...fujitsu.com" <lizf@...fujitsu.com>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [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@...fujitsu.com> wrote:

> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...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@...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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