lkml.org 
[lkml]   [2009]   [Sep]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH][rc1] cgroup: catch bad css refcnt at css_put
    On Mon, 28 Sep 2009 07:20:08 -0700
    Paul Menage <menage@google.com> wrote:

    > On Mon, Sep 28, 2009 at 2:13 AM, KAMEZAWA Hiroyuki
    > <kamezawa.hiroyu@jp.fujitsu.com> wrote:
    > > This is a patch for checking css->refcnt's sanity at css_put().
    > >
    > > BTW, I noticed that...css->refcnt may overflow if used with memcg...
    > > Now, refcnt is incremented per a page. Paul, do you have any idea ?
    > > (Ah, yes. "don't use css->refcnt per page" is maybe reasonable but
    > >  it will be big change..)
    > >
    > > ==
    > > __css_put() doesn't check a bug as refcnt goes to minus.
    > > I think it should be caught. This patch adds a check for it.
    > >
    > > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    >
    > Acked-by: Paul Menage <menage@google.com>
    >
    Thanks.

    > Looks reasonable, although there's no guarantee that it will warn on a
    > buggy release rather than a correct release that occur after a buggy
    > release.
    >
    yes, it's a problem of refcnt.

    Thanks,
    -Kame


    > > ---
    > >  kernel/cgroup.c |    5 ++++-
    > >  1 file changed, 4 insertions(+), 1 deletion(-)
    > >
    > > Index: linux-2.6.32-rc1/kernel/cgroup.c
    > > ===================================================================
    > > --- linux-2.6.32-rc1.orig/kernel/cgroup.c
    > > +++ linux-2.6.32-rc1/kernel/cgroup.c
    > > @@ -3708,8 +3708,10 @@ static void check_for_release(struct cgr
    > >  void __css_put(struct cgroup_subsys_state *css)
    > >  {
    > >        struct cgroup *cgrp = css->cgroup;
    > > +       int val;
    > >        rcu_read_lock();
    > > -       if (atomic_dec_return(&css->refcnt) == 1) {
    > > +       val = atomic_dec_return(&css->refcnt);
    > > +       if (val == 1) {
    > >                if (notify_on_release(cgrp)) {
    > >                        set_bit(CGRP_RELEASABLE, &cgrp->flags);
    > >                        check_for_release(cgrp);
    > > @@ -3717,6 +3719,7 @@ void __css_put(struct cgroup_subsys_stat
    > >                cgroup_wakeup_rmdir_waiter(cgrp);
    > >        }
    > >        rcu_read_unlock();
    > > +       WARN_ON(val < 1);
    > >  }
    > >
    > >  /*
    > >
    > >
    >

    --
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2009-09-29 05:11    [W:3.460 / U:0.012 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site