linux-kernel - Re: [PATCH 6/7] cgroups: Warn if a bindable subsystem calls css

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Message-ID: <AANLkTi=wS8aOuVQ-WBPGyP24oAigAqeZxKgAtpw8PnZY@mail.gmail.com>
Date:	Thu, 28 Oct 2010 17:05:05 -0700
From:	Paul Menage <menage@...gle.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	"akpm >> Andrew Morton" <akpm@...ux-foundation.org>,
	Stephane Eranian <eranian@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	containers@...ts.linux-foundation.org
Subject: Re: [PATCH 6/7] cgroups: Warn if a bindable subsystem calls css_get()

Maybe re-title this patch to BUG() if a bindable subsystem calls css_get() ?

Paul

On Fri, Oct 22, 2010 at 1:12 AM, Li Zefan <lizf@...fujitsu.com> wrote:
> For now bindable subsystems should not use css_get/put(), so warn
> on this misuse.
>
> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
> ---
>  include/linux/cgroup.h |    7 +++++--
>  kernel/cgroup.c        |    3 +++
>  2 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index 1e4e1df..10e4e02 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -80,13 +80,15 @@ struct cgroup_subsys_state {
>
>  /* bits in struct cgroup_subsys_state flags field */
>  enum {
> -       CSS_ROOT, /* This CSS is the root of the subsystem */
> -       CSS_REMOVED, /* This CSS is dead */
> +       CSS_ROOT,       /* This CSS is the root of the subsystem */
> +       CSS_REMOVED,    /* This CSS is dead */
> +       CSS_NO_GET,     /* Forbid calling css_get/put() */
>  };
>
>  /* Caller must verify that the css is not for root cgroup */
>  static inline void __css_get(struct cgroup_subsys_state *css, int count)
>  {
> +       BUG_ON(test_bit(CSS_NO_GET, &css->flags));
>        atomic_add(count, &css->refcnt);
>  }
>
> @@ -119,6 +121,7 @@ static inline bool css_tryget(struct cgroup_subsys_state *css)
>  {
>        if (test_bit(CSS_ROOT, &css->flags))
>                return true;
> +       BUG_ON(test_bit(CSS_NO_GET, &css->flags));
>        while (!atomic_inc_not_zero(&css->refcnt)) {
>                if (test_bit(CSS_REMOVED, &css->flags))
>                        return false;
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 12c1f7c..88e265d 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -936,6 +936,9 @@ static void init_cgroup_css(struct cgroup_subsys_state *css,
>        css->cgroup = cgrp;
>        atomic_set(&css->refcnt, 1);
>        css->flags = 0;
> +       /* For now, a bindable subsystem should not call css_get/put(). */
> +       if (ss->can_bind)
> +               set_bit(CSS_NO_GET, &css->flags);
>        css->id = NULL;
>        if (cgrp == dummytop)
>                set_bit(CSS_ROOT, &css->flags);
> --
> 1.7.0.1
>
>
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