+extern int rcu_pending(int cpu);
+extern int rcu_needs_cpu(int cpu);
+
+/**
+ * rcu_read_lock - mark the beginning of an RCU read-side critical section.
+ *
+ * When synchronize_rcu() is invoked on one CPU while other CPUs
+ * are within RCU read-side critical sections, then the
+ * synchronize_rcu() is guaranteed to block until after all the other
+ * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
+ * on one CPU while other CPUs are within RCU read-side critical
+ * sections, invocation of the corresponding RCU callback is deferred
+ * until after the all the other CPUs exit their critical sections.
+ *
+ * Note, however, that RCU callbacks are permitted to run concurrently
+ * with RCU read-side critical sections. One way that this can happen
+ * is via the following sequence of events: (1) CPU 0 enters an RCU
+ * read-side critical section, (2) CPU 1 invokes call_rcu() to register
+ * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
+ * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
+ * callback is invoked. This is legal, because the RCU read-side critical
+ * section that was running concurrently with the call_rcu() (and which
+ * therefore might be referencing something that the corresponding RCU
+ * callback would free up) has completed before the corresponding
+ * RCU callback is invoked.
+ *
+ * RCU read-side critical sections may be nested. Any deferred actions
+ * will be deferred until the outermost RCU read-side critical section
+ * completes.
+ *
+ * It is illegal to block while in an RCU read-side critical section.
+ */
+#define rcu_read_lock() \
+ do { \
+ preempt_disable(); \
+ __acquire(RCU); \
+ } while(0)
+
+/**
+ * rcu_read_unlock - marks the end of an RCU read-side critical section.
+ *
+ * See rcu_read_lock() for more information.
+ */
+#define rcu_read_unlock() \
+ do { \
+ __release(RCU); \
+ preempt_enable(); \
+ } while(0)
+
+/*
+ * So where is rcu_write_lock()? It does not exist, as there is no
+ * way for writers to lock out RCU readers. This is a feature, not
+ * a bug -- this property is what provides RCU's performance benefits.
+ * Of course, writers must coordinate with each other. The normal
+ * spinlock primitives work well for this, but any other technique may be
+ * used as well. RCU does not care how the writers keep out of each
+ * others' way, as long as they do so.
+ */
+
+/**
+ * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
+ *
+ * This is equivalent of rcu_read_lock(), but to be used when updates
+ * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
+ * consider completion of a softirq handler to be a quiescent state,
+ * a process in RCU read-side critical section must be protected by
+ * disabling softirqs. Read-side critical sections in interrupt context
+ * can use just rcu_read_lock().
+ *
+ */
+#define rcu_read_lock_bh() \
+ do { \
+ local_bh_disable(); \
+ __acquire(RCU_BH); \
+ } while(0)
+
+/*
+ * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
+ *
+ * See rcu_read_lock_bh() for more information.
+ */
+#define rcu_read_unlock_bh() \
+ do { \
+ __release(RCU_BH); \
+ local_bh_enable(); \
+ } while(0)
+
+/**
+ * rcu_dereference - fetch an RCU-protected pointer in an
+ * RCU read-side critical section. This pointer may later
+ * be safely dereferenced.
+ *
+ * Inserts memory barriers on architectures that require them
+ * (currently only the Alpha), and, more importantly, documents
+ * exactly which pointers are protected by RCU.
+ */
+
+#define rcu_dereference(p) ({ \
+ typeof(p) _________p1 = p; \
+ smp_read_barrier_depends(); \
+ (_________p1); \
+ })
+
+/**
+ * rcu_assign_pointer - assign (publicize) a pointer to a newly
+ * initialized structure that will be dereferenced by RCU read-side
+ * critical sections. Returns the value assigned.
+ *
+ * Inserts memory barriers on architectures that require them
+ * (pretty much all of them other than x86), and also prevents
+ * the compiler from reordering the code that initializes the
+ * structure after the pointer assignment. More importantly, this
+ * call documents which pointers will be dereferenced by RCU read-side
+ * code.
+ */
+
+#define rcu_assign_pointer(p, v) ({ \
+ smp_wmb(); \
+ (p) = (v); \
+ })
+
+/**
+ * synchronize_sched - block until all CPUs have exited any non-preemptive
+ * kernel code sequences.
+ *
+ * This means that all preempt_disable code sequences, including NMI and
+ * hardware-interrupt handlers, in progress on entry will have completed
+ * before this primitive returns. However, this does not guarantee that
+ * softirq handlers will have completed, since in some kernels, these
+ * handlers can run in process context, and can block.
+ *
+ * This primitive provides the guarantees made by the (now removed)
+ * synchronize_kernel() API. In contrast, synchronize_rcu() only
+ * guarantees that rcu_read_lock() sections will have completed.
+ * In "classic RCU", these two guarantees happen to be one and
+ * the same, but can differ in realtime RCU implementations.
+ */
+#define synchronize_sched() synchronize_rcu()