Messages in this thread | | | Date | Tue, 29 Sep 2009 12:06:05 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [PATCH][rc1] cgroup: catch bad css refcnt at css_put |
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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); > > } > > > > /* > > > > >
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