1 files changed, 32 insertions, 0 deletions

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 872a98e13d6a..8fe86609441f 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -209,13 +209,45 @@ static inline int rcu_read_lock_sched_held(void)
                 rcu_dereference_raw(p); \
         })
 
+/**
+ * rcu_dereference_protected - fetch RCU pointer when updates prevented
+ *
+ * Return the value of the specified RCU-protected pointer, but omit
+ * both the smp_read_barrier_depends() and the ACCESS_ONCE().  This
+ * is useful in cases where update-side locks prevent the value of the
+ * pointer from changing.  Please note that this primitive does -not-
+ * prevent the compiler from repeating this reference or combining it
+ * with other references, so it should not be used without protection
+ * of appropriate locks.
+ */
+#define rcu_dereference_protected(p, c) \
+        ({ \
+                if (debug_lockdep_rcu_enabled() && !(c)) \
+                        lockdep_rcu_dereference(__FILE__, __LINE__); \
+                (p); \
+        })
+
 #else /* #ifdef CONFIG_PROVE_RCU */
 
 #define rcu_dereference_check(p, c)     rcu_dereference_raw(p)
+#define rcu_dereference_protected(p, c) (p)
 
 #endif /* #else #ifdef CONFIG_PROVE_RCU */
 
 /**
+ * rcu_access_pointer - fetch RCU pointer with no dereferencing
+ *
+ * Return the value of the specified RCU-protected pointer, but omit the
+ * smp_read_barrier_depends() and keep the ACCESS_ONCE().  This is useful
+ * when the value of this pointer is accessed, but the pointer is not
+ * dereferenced, for example, when testing an RCU-protected pointer against
+ * NULL.  This may also be used in cases where update-side locks prevent
+ * the value of the pointer from changing, but rcu_dereference_protected()
+ * is a lighter-weight primitive for this use case.
+ */
+#define rcu_access_pointer(p)   ACCESS_ONCE(p)
+
+/**
  * rcu_read_lock - mark the beginning of an RCU read-side critical section.
  *
  * When synchronize_rcu() is invoked on one CPU while other CPUs