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

Arnd Bergmann
2010-09-07T20:00:58Z

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.

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)); \
})