--- zzzz-none-000/linux-2.6.32.61/include/linux/rcupdate.h	2013-06-10 09:43:48.000000000 +0000
+++ ar10-7272-687/linux-2.6.32.61/include/linux/rcupdate.h	2014-08-12 13:03:17.000000000 +0000
@@ -305,4 +305,121 @@
 extern void call_rcu_bh(struct rcu_head *head,
 			void (*func)(struct rcu_head *head));
 
+
+/* AVM: backport from v3.15 */
+/*
+ * Helper functions for rcu_dereference_check(), rcu_dereference_protected()
+ * and rcu_assign_pointer().  Some of these could be folded into their
+ * callers, but they are left separate in order to ease introduction of
+ * multiple flavors of pointers to match the multiple flavors of RCU
+ * (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
+ * the future.
+ */
+
+#define rcu_lockdep_assert(c, msg)
+
+#ifdef __CHECKER__
+#define rcu_dereference_sparse(p, space) \
+    ((void)(((typeof(*p) space *)p) == p))
+#else /* #ifdef __CHECKER__ */
+#define rcu_dereference_sparse(p, space)
+#endif /* #else #ifdef __CHECKER__ */
+
+#define __rcu_access_pointer(p, space) \
+({ \
+    typeof(*p) *_________p1 = (typeof(*p) *__force)ACCESS_ONCE(p); \
+    rcu_dereference_sparse(p, space); \
+    ((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, "suspicious rcu_dereference_check() usage"); \
+    rcu_dereference_sparse(p, space); \
+    smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
+    ((typeof(*p) __force __kernel *)(_________p1)); \
+})
+#define __rcu_dereference_protected(p, c, space) \
+({ \
+    rcu_lockdep_assert(c, "suspicious rcu_dereference_protected() usage"); \
+    rcu_dereference_sparse(p, space); \
+    ((typeof(*p) __force __kernel *)(p)); \
+})
+
+#define __rcu_access_index(p, space) \
+({ \
+    typeof(p) _________p1 = ACCESS_ONCE(p); \
+    rcu_dereference_sparse(p, space); \
+    (_________p1); \
+})
+#define __rcu_dereference_index_check(p, c) \
+({ \
+    typeof(p) _________p1 = ACCESS_ONCE(p); \
+    rcu_lockdep_assert(c, \
+               "suspicious rcu_dereference_index_check() usage"); \
+    smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
+    (_________p1); \
+})
+
+
+/**
+ * rcu_dereference_check() - rcu_dereference with debug checking
+ * @p: The pointer to read, prior to dereferencing
+ * @c: The conditions under which the dereference will take place
+ *
+ * Do an rcu_dereference(), but check that the conditions under which the
+ * dereference will take place are correct.  Typically the conditions
+ * indicate the various locking conditions that should be held at that
+ * point.  The check should return true if the conditions are satisfied.
+ * An implicit check for being in an RCU read-side critical section
+ * (rcu_read_lock()) is included.
+ *
+ * For example:
+ *
+ *  bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
+ *
+ * could be used to indicate to lockdep that foo->bar may only be dereferenced
+ * if either rcu_read_lock() is held, or that the lock required to replace
+ * the bar struct at foo->bar is held.
+ *
+ * Note that the list of conditions may also include indications of when a lock
+ * need not be held, for example during initialisation or destruction of the
+ * target struct:
+ *
+ *  bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
+ *                        atomic_read(&foo->usage) == 0);
+ *
+ * Inserts memory barriers on architectures that require them
+ * (currently only the Alpha), prevents the compiler from refetching
+ * (and from merging fetches), and, more importantly, documents exactly
+ * which pointers are protected by RCU and checks that the pointer is
+ * annotated as __rcu.
+ */
+#define rcu_dereference_check(p, c) \
+    __rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)
+/**
+ * rcu_dereference_protected() - fetch RCU pointer when updates prevented
+ * @p: The pointer to read, prior to dereferencing
+ * @c: The conditions under which the dereference will take place
+ *
+ * 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.
+ *
+ * This function is only for update-side use.  Using this function
+ * when protected only by rcu_read_lock() will result in infrequent
+ * but very ugly failures.
+ */
+#define rcu_dereference_protected(p, c) \
+    __rcu_dereference_protected((p), (c), __rcu)
+
+/* +++
+ * AVM: not present in 2.6.32,
+ */
+#define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/
+
 #endif /* __LINUX_RCUPDATE_H */