Re: [PATCH] md: do not use ++ in rcu_dereference() argument
From: Arnd Bergmann <arnd@arndb.de>
Date: 2010-09-07 20:01:07
Also in:
kernel-janitors, lkml
Subsystem:
read-copy update (rcu), the rest · Maintainers:
"Paul E. McKenney", Frederic Weisbecker, Neeraj Upadhyay, Joel Fernandes, Josh Triplett, Boqun Feng, Uladzislau Rezki, Linus Torvalds
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)); \ })