1 files changed, 27 insertions, 1 deletions

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index fe17d7d750c2..cc24a01df940 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -41,6 +41,7 @@
 #include <linux/percpu.h>
 #include <linux/cpumask.h>
 #include <linux/seqlock.h>
+#include <linux/lockdep.h>
 
 /**
  * struct rcu_head - callback structure for use with RCU
@@ -133,6 +134,15 @@ static inline void rcu_bh_qsctr_inc(int cpu)
 extern int rcu_pending(int cpu);
 extern int rcu_needs_cpu(int cpu);
 
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+extern struct lockdep_map rcu_lock_map;
+# define rcu_read_acquire()     lock_acquire(&rcu_lock_map, 0, 0, 2, 1, _THIS_IP_)
+# define rcu_read_release()     lock_release(&rcu_lock_map, 1, _THIS_IP_)
+#else
+# define rcu_read_acquire()     do { } while (0)
+# define rcu_read_release()     do { } while (0)
+#endif
+
 /**
  * rcu_read_lock - mark the beginning of an RCU read-side critical section.
  *
@@ -166,6 +176,7 @@ extern int rcu_needs_cpu(int cpu);
         do { \
                 preempt_disable(); \
                 __acquire(RCU); \
+                rcu_read_acquire(); \
         } while(0)
 
 /**
@@ -175,6 +186,7 @@ extern int rcu_needs_cpu(int cpu);
  */
 #define rcu_read_unlock() \
         do { \
+                rcu_read_release(); \
                 __release(RCU); \
                 preempt_enable(); \
         } while(0)
@@ -204,6 +216,7 @@ extern int rcu_needs_cpu(int cpu);
         do { \
                 local_bh_disable(); \
                 __acquire(RCU_BH); \
+                rcu_read_acquire(); \
         } while(0)
 
 /*
@@ -213,10 +226,23 @@ extern int rcu_needs_cpu(int cpu);
  */
 #define rcu_read_unlock_bh() \
         do { \
+                rcu_read_release(); \
                 __release(RCU_BH); \
                 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
@@ -228,7 +254,7 @@ extern int rcu_needs_cpu(int cpu);
  */
 
 #define rcu_dereference(p)     ({ \
-                                typeof(p) _________p1 = p; \
+                                typeof(p) _________p1 = ACCESS_ONCE(p); \
                                 smp_read_barrier_depends(); \
                                 (_________p1); \
                                 })