Re: [PATCH] md: do not use ++ in rcu_dereference() argument

Paul E. McKenney
2010-09-07T20:50:15Z

On Tue, Sep 07, 2010 at 10:00:58PM +0200, Arnd Bergmann wrote:
> On Tuesday 07 September 2010 21:21:55 Kulikov Vasiliy wrote:
> > #define __rcu_dereference_check(p, c, space) \
> > ({ \
> > typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
> > ^
> > rcu_lockdep_assert(c); \
> > (void) (((typeof (*p) space *)p) = p); \
> > ^ ^
> > smp_read_barrier_depends(); \
> > ((typeof(*p) __force __kernel *)(_________p1)); \
> > })
> >
> > If I understand this, it is evaluated three times, right?
>
> Yes, that looks like my own fault, I added that :(
>
> This patch seems to fix it, but I need to think about it some more
> to make sure it still does everything we need.

Let me know when you are satisfied with it, and then I will pick it up.

Thanx, Paul

> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 89414d6..743bc3f 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -313,21 +313,21 @@ extern int rcu_my_thread_group_empty(void);
> #define __rcu_access_pointer(p, space) \
> ({ \
> typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
> - (void) (((typeof (*p) space *)p) = p); \
> + (void) (((typeof (*p) space *)NULL) = (typeof(p))NULL); \
> ((typeof(*p) __force __kernel *)(_________p1)); \
> })
> #define __rcu_dereference_check(p, c, space) \
> ({ \
> typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
> rcu_lockdep_assert(c); \
> - (void) (((typeof (*p) space *)p) = p); \
> + (void) (((typeof (*p) space *)NULL) = (typeof(p))NULL); \
> smp_read_barrier_depends(); \
> ((typeof(*p) __force __kernel *)(_________p1)); \
> })
> #define __rcu_dereference_protected(p, c, space) \
> ({ \
> rcu_lockdep_assert(c); \
> - (void) (((typeof (*p) space *)p) = p); \
> + (void) (((typeof (*p) space *)NULL) = (typeof(p))NULL); \
> ((typeof(*p) __force __kernel *)(p)); \
> })
>