diff --git a/ap/os/linux/linux-3.4.x/kernel/srcu.c b/ap/os/linux/linux-3.4.x/kernel/srcu.c
new file mode 100644
index 0000000..ba35f3a
--- /dev/null
+++ b/ap/os/linux/linux-3.4.x/kernel/srcu.c
@@ -0,0 +1,328 @@
+/*
+ * Sleepable Read-Copy Update mechanism for mutual exclusion.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (C) IBM Corporation, 2006
+ *
+ * Author: Paul McKenney <paulmck@us.ibm.com>
+ *
+ * For detailed explanation of Read-Copy Update mechanism see -
+ * 		Documentation/RCU/ *.txt
+ *
+ */
+
+#include <linux/export.h>
+#include <linux/mutex.h>
+#include <linux/percpu.h>
+#include <linux/preempt.h>
+#include <linux/rcupdate.h>
+#include <linux/sched.h>
+#include <linux/smp.h>
+#include <linux/delay.h>
+#include <linux/srcu.h>
+
+static int init_srcu_struct_fields(struct srcu_struct *sp)
+{
+	sp->completed = 0;
+	mutex_init(&sp->mutex);
+	sp->per_cpu_ref = alloc_percpu(struct srcu_struct_array);
+	return sp->per_cpu_ref ? 0 : -ENOMEM;
+}
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+
+int __init_srcu_struct(struct srcu_struct *sp, const char *name,
+		       struct lock_class_key *key)
+{
+	/* Don't re-initialize a lock while it is held. */
+	debug_check_no_locks_freed((void *)sp, sizeof(*sp));
+	lockdep_init_map(&sp->dep_map, name, key, 0);
+	return init_srcu_struct_fields(sp);
+}
+EXPORT_SYMBOL_GPL(__init_srcu_struct);
+
+#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+
+/**
+ * init_srcu_struct - initialize a sleep-RCU structure
+ * @sp: structure to initialize.
+ *
+ * Must invoke this on a given srcu_struct before passing that srcu_struct
+ * to any other function.  Each srcu_struct represents a separate domain
+ * of SRCU protection.
+ */
+int init_srcu_struct(struct srcu_struct *sp)
+{
+	return init_srcu_struct_fields(sp);
+}
+EXPORT_SYMBOL_GPL(init_srcu_struct);
+
+#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
+
+/*
+ * srcu_readers_active_idx -- returns approximate number of readers
+ *	active on the specified rank of per-CPU counters.
+ */
+
+static int srcu_readers_active_idx(struct srcu_struct *sp, int idx)
+{
+	int cpu;
+	int sum;
+
+	sum = 0;
+	for_each_possible_cpu(cpu)
+		sum += per_cpu_ptr(sp->per_cpu_ref, cpu)->c[idx];
+	return sum;
+}
+
+/**
+ * srcu_readers_active - returns approximate number of readers.
+ * @sp: which srcu_struct to count active readers (holding srcu_read_lock).
+ *
+ * Note that this is not an atomic primitive, and can therefore suffer
+ * severe errors when invoked on an active srcu_struct.  That said, it
+ * can be useful as an error check at cleanup time.
+ */
+static int srcu_readers_active(struct srcu_struct *sp)
+{
+	return srcu_readers_active_idx(sp, 0) + srcu_readers_active_idx(sp, 1);
+}
+
+/**
+ * cleanup_srcu_struct - deconstruct a sleep-RCU structure
+ * @sp: structure to clean up.
+ *
+ * Must invoke this after you are finished using a given srcu_struct that
+ * was initialized via init_srcu_struct(), else you leak memory.
+ */
+void cleanup_srcu_struct(struct srcu_struct *sp)
+{
+	int sum;
+
+	sum = srcu_readers_active(sp);
+	WARN_ON(sum);  /* Leakage unless caller handles error. */
+	if (sum != 0)
+		return;
+	free_percpu(sp->per_cpu_ref);
+	sp->per_cpu_ref = NULL;
+}
+EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
+
+/*
+ * Counts the new reader in the appropriate per-CPU element of the
+ * srcu_struct.  Must be called from process context.
+ * Returns an index that must be passed to the matching srcu_read_unlock().
+ */
+int __srcu_read_lock(struct srcu_struct *sp)
+{
+	int idx;
+
+	preempt_disable();
+	idx = sp->completed & 0x1;
+	barrier();  /* ensure compiler looks -once- at sp->completed. */
+	per_cpu_ptr(sp->per_cpu_ref, smp_processor_id())->c[idx]++;
+	srcu_barrier();  /* ensure compiler won't misorder critical section. */
+	preempt_enable();
+	return idx;
+}
+EXPORT_SYMBOL_GPL(__srcu_read_lock);
+
+/*
+ * Removes the count for the old reader from the appropriate per-CPU
+ * element of the srcu_struct.  Note that this may well be a different
+ * CPU than that which was incremented by the corresponding srcu_read_lock().
+ * Must be called from process context.
+ */
+void __srcu_read_unlock(struct srcu_struct *sp, int idx)
+{
+	preempt_disable();
+	srcu_barrier();  /* ensure compiler won't misorder critical section. */
+	per_cpu_ptr(sp->per_cpu_ref, smp_processor_id())->c[idx]--;
+	preempt_enable();
+}
+EXPORT_SYMBOL_GPL(__srcu_read_unlock);
+
+/*
+ * We use an adaptive strategy for synchronize_srcu() and especially for
+ * synchronize_srcu_expedited().  We spin for a fixed time period
+ * (defined below) to allow SRCU readers to exit their read-side critical
+ * sections.  If there are still some readers after 10 microseconds,
+ * we repeatedly block for 1-millisecond time periods.  This approach
+ * has done well in testing, so there is no need for a config parameter.
+ */
+#define SYNCHRONIZE_SRCU_READER_DELAY 10
+
+/*
+ * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
+ */
+static void __synchronize_srcu(struct srcu_struct *sp, void (*sync_func)(void))
+{
+	int idx;
+
+	rcu_lockdep_assert(!lock_is_held(&sp->dep_map) &&
+			   !lock_is_held(&rcu_bh_lock_map) &&
+			   !lock_is_held(&rcu_lock_map) &&
+			   !lock_is_held(&rcu_sched_lock_map),
+			   "Illegal synchronize_srcu() in same-type SRCU (or RCU) read-side critical section");
+
+	idx = sp->completed;
+	mutex_lock(&sp->mutex);
+
+	/*
+	 * Check to see if someone else did the work for us while we were
+	 * waiting to acquire the lock.  We need -two- advances of
+	 * the counter, not just one.  If there was but one, we might have
+	 * shown up -after- our helper's first synchronize_sched(), thus
+	 * having failed to prevent CPU-reordering races with concurrent
+	 * srcu_read_unlock()s on other CPUs (see comment below).  So we
+	 * either (1) wait for two or (2) supply the second ourselves.
+	 */
+
+	if ((sp->completed - idx) >= 2) {
+		mutex_unlock(&sp->mutex);
+		return;
+	}
+
+	sync_func();  /* Force memory barrier on all CPUs. */
+
+	/*
+	 * The preceding synchronize_sched() ensures that any CPU that
+	 * sees the new value of sp->completed will also see any preceding
+	 * changes to data structures made by this CPU.  This prevents
+	 * some other CPU from reordering the accesses in its SRCU
+	 * read-side critical section to precede the corresponding
+	 * srcu_read_lock() -- ensuring that such references will in
+	 * fact be protected.
+	 *
+	 * So it is now safe to do the flip.
+	 */
+
+	idx = sp->completed & 0x1;
+	sp->completed++;
+
+	sync_func();  /* Force memory barrier on all CPUs. */
+
+	/*
+	 * At this point, because of the preceding synchronize_sched(),
+	 * all srcu_read_lock() calls using the old counters have completed.
+	 * Their corresponding critical sections might well be still
+	 * executing, but the srcu_read_lock() primitives themselves
+	 * will have finished executing.  We initially give readers
+	 * an arbitrarily chosen 10 microseconds to get out of their
+	 * SRCU read-side critical sections, then loop waiting 1/HZ
+	 * seconds per iteration.  The 10-microsecond value has done
+	 * very well in testing.
+	 */
+
+	if (srcu_readers_active_idx(sp, idx))
+		udelay(SYNCHRONIZE_SRCU_READER_DELAY);
+	while (srcu_readers_active_idx(sp, idx))
+		schedule_timeout_interruptible(1);
+
+	sync_func();  /* Force memory barrier on all CPUs. */
+
+	/*
+	 * The preceding synchronize_sched() forces all srcu_read_unlock()
+	 * primitives that were executing concurrently with the preceding
+	 * for_each_possible_cpu() loop to have completed by this point.
+	 * More importantly, it also forces the corresponding SRCU read-side
+	 * critical sections to have also completed, and the corresponding
+	 * references to SRCU-protected data items to be dropped.
+	 *
+	 * Note:
+	 *
+	 *	Despite what you might think at first glance, the
+	 *	preceding synchronize_sched() -must- be within the
+	 *	critical section ended by the following mutex_unlock().
+	 *	Otherwise, a task taking the early exit can race
+	 *	with a srcu_read_unlock(), which might have executed
+	 *	just before the preceding srcu_readers_active() check,
+	 *	and whose CPU might have reordered the srcu_read_unlock()
+	 *	with the preceding critical section.  In this case, there
+	 *	is nothing preventing the synchronize_sched() task that is
+	 *	taking the early exit from freeing a data structure that
+	 *	is still being referenced (out of order) by the task
+	 *	doing the srcu_read_unlock().
+	 *
+	 *	Alternatively, the comparison with "2" on the early exit
+	 *	could be changed to "3", but this increases synchronize_srcu()
+	 *	latency for bulk loads.  So the current code is preferred.
+	 */
+
+	mutex_unlock(&sp->mutex);
+}
+
+/**
+ * synchronize_srcu - wait for prior SRCU read-side critical-section completion
+ * @sp: srcu_struct with which to synchronize.
+ *
+ * Flip the completed counter, and wait for the old count to drain to zero.
+ * As with classic RCU, the updater must use some separate means of
+ * synchronizing concurrent updates.  Can block; must be called from
+ * process context.
+ *
+ * Note that it is illegal to call synchronize_srcu() from the corresponding
+ * SRCU read-side critical section; doing so will result in deadlock.
+ * However, it is perfectly legal to call synchronize_srcu() on one
+ * srcu_struct from some other srcu_struct's read-side critical section.
+ */
+void synchronize_srcu(struct srcu_struct *sp)
+{
+	__synchronize_srcu(sp, synchronize_sched);
+}
+EXPORT_SYMBOL_GPL(synchronize_srcu);
+
+/**
+ * synchronize_srcu_expedited - Brute-force SRCU grace period
+ * @sp: srcu_struct with which to synchronize.
+ *
+ * Wait for an SRCU grace period to elapse, but use a "big hammer"
+ * approach to force the grace period to end quickly.  This consumes
+ * significant time on all CPUs and is unfriendly to real-time workloads,
+ * so is thus not recommended for any sort of common-case code.  In fact,
+ * if you are using synchronize_srcu_expedited() in a loop, please
+ * restructure your code to batch your updates, and then use a single
+ * synchronize_srcu() instead.
+ *
+ * Note that it is illegal to call this function while holding any lock
+ * that is acquired by a CPU-hotplug notifier.  And yes, it is also illegal
+ * to call this function from a CPU-hotplug notifier.  Failing to observe
+ * these restriction will result in deadlock.  It is also illegal to call
+ * synchronize_srcu_expedited() from the corresponding SRCU read-side
+ * critical section; doing so will result in deadlock.  However, it is
+ * perfectly legal to call synchronize_srcu_expedited() on one srcu_struct
+ * from some other srcu_struct's read-side critical section, as long as
+ * the resulting graph of srcu_structs is acyclic.
+ */
+void synchronize_srcu_expedited(struct srcu_struct *sp)
+{
+	__synchronize_srcu(sp, synchronize_sched_expedited);
+}
+EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
+
+/**
+ * srcu_batches_completed - return batches completed.
+ * @sp: srcu_struct on which to report batch completion.
+ *
+ * Report the number of batches, correlated with, but not necessarily
+ * precisely the same as, the number of grace periods that have elapsed.
+ */
+
+long srcu_batches_completed(struct srcu_struct *sp)
+{
+	return sp->completed;
+}
+EXPORT_SYMBOL_GPL(srcu_batches_completed);