Frederic Weisbecker (fweisbec@xxxxxxxxx) wrote:
> On Wed, Dec 21, 2011 at 02:08:48PM +0100, Oleg Nesterov wrote:
> > On 12/21, Frederic Weisbecker wrote:
> > > Hi,
> > >
> > > Starring at some parts of cgroups, I have a few questions:
> > >
> > > - Is cgroup_enable_task_cg_list()'s while_each_thread() safe
> > > against concurrent exec()? The leader may change in de_thread()
> > > and invalidate the test done in while_each_thread().
> >
> > Yes. Oh, we need to do something with while_each_thread.
>
> Would something like this work?
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index c0c5876..e002a00 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -2293,8 +2293,12 @@ extern bool current_is_single_threaded(void);
> #define do_each_thread(g, t) \
> for (g = t = &init_task ; (g = t = next_task(g)) != &init_task ; ) do
>
> -#define while_each_thread(g, t) \
> - while ((t = next_thread(t)) != g)
> +#define while_each_thread(g, t) \
> + while (({ \
> + struct task_struct *__prev = t; \
> + t = next_thread(t); \
> + t != __prev && t != g; \
Hi,
Don't you still have an (highly unlikely) race if you exec
and then pthread_create()?
Instead of:
t != __prev && t != g;
How about:
t != t->group_leader;
Regards,
Mandeep
> + }))
>
> static inline int get_nr_threads(struct task_struct *tsk)
> {
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