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SubjectRe: [PATCH] cpuset: current_cpuset_is_being_rebound() need rcu lock
On Fri, Mar 12, 2010 at 09:03:03AM +0900, KOSAKI Motohiro wrote:
> > On Thu, Mar 11, 2010 at 02:46:15PM +0900, KOSAKI Motohiro wrote:
> > > rcu lockdep detected cpuset have wrong rcu usage.
> > > the fixing is trivial. but I wonder why don't cpuset_being_rebound assignment
> > > and read need a memory barrier pairing?
> >
> > The fix is in -tip, commit 99ee4ca746dda71326db7645463b4075ac1d665c.
> >
> > This is an initialization-time use of rcu_dereference(), so no other
> > task has a reference to this data. Hence it is constant. Other uses
> > of this code operate on shared data structures, which might change at
> > any time.
>
> thanks. I haven't notice such commit.
>
> I think you are talking about task_cs(current) accessing and you are right
> in such point.
> but I'm talking cpuset_being_rebound global variable.
>
> update_tasks_nodemask() has following code
>
> static void update_tasks_nodemask(struct cpuset *cs, const nodemask_t *oldmem,
> struct ptr_heap *heap)
> {
> cpuset_being_rebound = cs; /* start transaction */
> cgroup_scan_tasks(&scan);
> cpuset_being_rebound = NULL; /* end transaction */
> }

Hmmm... What commit are you looking at in what tree? I instead see
a much larger function body for update_tasks_nodemask(). I am looking
in a number of places, including 522dba7134d6b2e5821d3457f7941ec34f668e6d
in Linus's git tree.

Thanx, Paul


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