Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/shaggy...

[pandora-kernel.git] / include / linux / rcupdate.h

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 76c1a53..cc24a01 100644 (file)
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -231,6 +231,18 @@ extern struct lockdep_map rcu_lock_map;
                local_bh_enable(); \
        } while(0)
 
+/*
+ * Prevent the compiler from merging or refetching accesses.  The compiler
+ * is also forbidden from reordering successive instances of ACCESS_ONCE(),
+ * but only when the compiler is aware of some particular ordering.  One way
+ * to make the compiler aware of ordering is to put the two invocations of
+ * ACCESS_ONCE() in different C statements.
+ *
+ * This macro does absolutely -nothing- to prevent the CPU from reordering,
+ * merging, or refetching absolutely anything at any time.
+ */
+#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
+
 /**
  * rcu_dereference - fetch an RCU-protected pointer in an
  * RCU read-side critical section.  This pointer may later
@@ -242,7 +254,7 @@ extern struct lockdep_map rcu_lock_map;
  */
 
 #define rcu_dereference(p)     ({ \
-                               typeof(p) _________p1 = p; \
+                               typeof(p) _________p1 = ACCESS_ONCE(p); \
                                smp_read_barrier_depends(); \
                                (_________p1); \
                                })