Re: [PATCH] rculist: list_first_or_null_rcu() should use list_entry_rcu()

Tejun Heo
2013-06-25T23:09:43Z

Hello, Paul.

On Tue, Jun 25, 2013 at 03:57:59PM -0700, Paul E. McKenney wrote:
> > #define list_first_or_null_rcu(ptr, type, member) \
> > ({struct list_head *__ptr = (ptr); \
> > - struct list_head __rcu *__next = list_next_rcu(__ptr); \
> > - likely(__ptr != __next) ? container_of(__next, type, member) : NULL; \
> > + struct list_head *__next = __ptr->next; \
> > + likely(__ptr != __next) ? \
> > + list_entry_rcu(__next, type, member) : NULL; \
>
> I am a bit uneasy with this, and would feel better if the volatile
> cast was on the very first fetch of the ->next pointer.
>
> Is there some reason why my unease is ill-founded?

Do you mean something like the following?

struct list_head *__next = ACCESS_ONCE(__ptr->next); \
likely(__ptr != __next) ? \
list_entry_rcu(__next, type, member) : NULL; \

Yeah, that looks right to me.

Thanks.

--
tejun