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SubjectRe: INFO: suspicious rcu_dereference_check() usage - include/linux/cgroup.h:492 invoked rcu_dereference_check() without protection!
On Wed, Apr 21, 2010 at 09:05:50AM +0800, Li Zefan wrote:
> > commit 2836f18139267ea918ed2cf39023fb0eb38c4361
> > Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > Date: Mon Apr 19 15:59:50 2010 -0700
> >
> > rcu: fix RCU lockdep splat on freezer_fork path
> >
> > Add an RCU read-side critical section to suppress this false positive.
> >
> > Located-by: Eric Paris <eparis@parisplace.org>
> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> >
> > diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
> > index da5e139..e5c0244 100644
> > --- a/kernel/cgroup_freezer.c
> > +++ b/kernel/cgroup_freezer.c
> > @@ -205,9 +205,12 @@ static void freezer_fork(struct cgroup_subsys *ss, struct task_struct *task)
> > * No lock is needed, since the task isn't on tasklist yet,
> > * so it can't be moved to another cgroup, which means the
> > * freezer won't be removed and will be valid during this
> > - * function call.
> > + * function call. Nevertheless, apply RCU read-side critical
> > + * section to suppress RCU lockdep false positives.
> > */
>
> It was me that added the original comment.
>
> > + rcu_read_lock();
> > freezer = task_freezer(task);
> > + rcu_read_unlock();
> >
> > /*
> > * The root cgroup is non-freezable, so we can skip the
>
> Acked-by: Li Zefan <lizf@cn.fujitsu.com>

Thank you, Li! I have added your Acked-by.

Thanx, Paul


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