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    SubjectRe: [PATCH 6/7] cgroups: Warn if a bindable subsystem calls css_get()
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    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@cn.fujitsu.com> wrote:
    > For now bindable subsystems should not use css_get/put(), so warn
    > on this misuse.
    >
    > Signed-off-by: Li Zefan <lizf@cn.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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