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diff --git a/contrib/userspace-rcu/static-wfstack.h b/contrib/userspace-rcu/static-wfstack.h
new file mode 100644
index 00000000000..29b81c3aac3
--- /dev/null
+++ b/contrib/userspace-rcu/static-wfstack.h
@@ -0,0 +1,455 @@
+#ifndef _URCU_STATIC_WFSTACK_H
+#define _URCU_STATIC_WFSTACK_H
+
+/*
+ * urcu/static/wfstack.h
+ *
+ * Userspace RCU library - Stack with with wait-free push, blocking traversal.
+ *
+ * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu/wfstack.h for
+ * linking dynamically with the userspace rcu library.
+ *
+ * Copyright 2010-2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/* Adapted from userspace-rcu 0.10 because version 0.7 doesn't support a stack
+ * without mutex. */
+
+#include <pthread.h>
+#include <assert.h>
+#include <poll.h>
+#include <stdbool.h>
+#include <urcu/compiler.h>
+#include <urcu/uatomic.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define CDS_WFS_END			((void *) 0x1UL)
+#define CDS_WFS_ADAPT_ATTEMPTS		10	/* Retry if being set */
+#define CDS_WFS_WAIT			10	/* Wait 10 ms if being set */
+
+/*
+ * Stack with wait-free push, blocking traversal.
+ *
+ * Stack implementing push, pop, pop_all operations, as well as iterator
+ * on the stack head returned by pop_all.
+ *
+ * Wait-free operations: cds_wfs_push, __cds_wfs_pop_all, cds_wfs_empty,
+ *                       cds_wfs_first.
+ * Blocking operations: cds_wfs_pop, cds_wfs_pop_all, cds_wfs_next,
+ *                      iteration on stack head returned by pop_all.
+ *
+ * Synchronization table:
+ *
+ * External synchronization techniques described in the API below is
+ * required between pairs marked with "X". No external synchronization
+ * required between pairs marked with "-".
+ *
+ *                      cds_wfs_push  __cds_wfs_pop  __cds_wfs_pop_all
+ * cds_wfs_push               -              -                  -
+ * __cds_wfs_pop              -              X                  X
+ * __cds_wfs_pop_all          -              X                  -
+ *
+ * cds_wfs_pop and cds_wfs_pop_all use an internal mutex to provide
+ * synchronization.
+ */
+
+/*
+ * cds_wfs_node_init: initialize wait-free stack node.
+ */
+static inline
+void _cds_wfs_node_init(struct cds_wfs_node *node)
+{
+	node->next = NULL;
+}
+
+/*
+ * __cds_wfs_init: initialize wait-free stack. Don't pair with
+ * any destroy function.
+ */
+static inline void ___cds_wfs_init(struct __cds_wfs_stack *s)
+{
+	s->head = CDS_WFS_END;
+}
+
+/*
+ * cds_wfs_init: initialize wait-free stack. Pair with
+ * cds_wfs_destroy().
+ */
+static inline
+void _cds_wfs_init(struct cds_wfs_stack *s)
+{
+	int ret;
+
+	s->head = CDS_WFS_END;
+	ret = pthread_mutex_init(&s->lock, NULL);
+	assert(!ret);
+}
+
+/*
+ * cds_wfs_destroy: destroy wait-free stack. Pair with
+ * cds_wfs_init().
+ */
+static inline
+void _cds_wfs_destroy(struct cds_wfs_stack *s)
+{
+	int ret = pthread_mutex_destroy(&s->lock);
+	assert(!ret);
+}
+
+static inline bool ___cds_wfs_end(void *node)
+{
+	return node == CDS_WFS_END;
+}
+
+/*
+ * cds_wfs_empty: return whether wait-free stack is empty.
+ *
+ * No memory barrier is issued. No mutual exclusion is required.
+ */
+static inline bool _cds_wfs_empty(cds_wfs_stack_ptr_t u_stack)
+{
+	struct __cds_wfs_stack *s = u_stack._s;
+
+	return ___cds_wfs_end(CMM_LOAD_SHARED(s->head));
+}
+
+/*
+ * cds_wfs_push: push a node into the stack.
+ *
+ * Issues a full memory barrier before push. No mutual exclusion is
+ * required.
+ *
+ * Returns 0 if the stack was empty prior to adding the node.
+ * Returns non-zero otherwise.
+ */
+static inline
+int _cds_wfs_push(cds_wfs_stack_ptr_t u_stack, struct cds_wfs_node *node)
+{
+	struct __cds_wfs_stack *s = u_stack._s;
+	struct cds_wfs_head *old_head, *new_head;
+
+	assert(node->next == NULL);
+	new_head = caa_container_of(node, struct cds_wfs_head, node);
+	/*
+	 * uatomic_xchg() implicit memory barrier orders earlier stores
+	 * to node (setting it to NULL) before publication.
+	 */
+	old_head = uatomic_xchg(&s->head, new_head);
+	/*
+	 * At this point, dequeuers see a NULL node->next, they should
+	 * busy-wait until node->next is set to old_head.
+	 */
+	CMM_STORE_SHARED(node->next, &old_head->node);
+	return !___cds_wfs_end(old_head);
+}
+
+/*
+ * Waiting for push to complete enqueue and return the next node.
+ */
+static inline struct cds_wfs_node *
+___cds_wfs_node_sync_next(struct cds_wfs_node *node, int blocking)
+{
+	struct cds_wfs_node *next;
+	int attempt = 0;
+
+	/*
+	 * Adaptative busy-looping waiting for push to complete.
+	 */
+	while ((next = CMM_LOAD_SHARED(node->next)) == NULL) {
+		if (!blocking)
+			return CDS_WFS_WOULDBLOCK;
+		if (++attempt >= CDS_WFS_ADAPT_ATTEMPTS) {
+			(void) poll(NULL, 0, CDS_WFS_WAIT);	/* Wait for 10ms */
+			attempt = 0;
+		} else {
+			caa_cpu_relax();
+		}
+	}
+
+	return next;
+}
+
+static inline
+struct cds_wfs_node *
+___cds_wfs_pop(cds_wfs_stack_ptr_t u_stack, int *state, int blocking)
+{
+	struct cds_wfs_head *head, *new_head;
+	struct cds_wfs_node *next;
+	struct __cds_wfs_stack *s = u_stack._s;
+
+	if (state)
+		*state = 0;
+	for (;;) {
+		head = CMM_LOAD_SHARED(s->head);
+		if (___cds_wfs_end(head)) {
+			return NULL;
+		}
+		next = ___cds_wfs_node_sync_next(&head->node, blocking);
+		if (!blocking && next == CDS_WFS_WOULDBLOCK) {
+			return CDS_WFS_WOULDBLOCK;
+		}
+		new_head = caa_container_of(next, struct cds_wfs_head, node);
+		if (uatomic_cmpxchg(&s->head, head, new_head) == head) {
+			if (state && ___cds_wfs_end(new_head))
+				*state |= CDS_WFS_STATE_LAST;
+			return &head->node;
+		}
+		if (!blocking) {
+			return CDS_WFS_WOULDBLOCK;
+		}
+		/* busy-loop if head changed under us */
+	}
+}
+
+/*
+ * __cds_wfs_pop_with_state_blocking: pop a node from the stack, with state.
+ *
+ * Returns NULL if stack is empty.
+ *
+ * __cds_wfs_pop_blocking needs to be synchronized using one of the
+ * following techniques:
+ *
+ * 1) Calling __cds_wfs_pop_blocking under rcu read lock critical
+ *    section. The caller must wait for a grace period to pass before
+ *    freeing the returned node or modifying the cds_wfs_node structure.
+ * 2) Using mutual exclusion (e.g. mutexes) to protect
+ *     __cds_wfs_pop_blocking and __cds_wfs_pop_all callers.
+ * 3) Ensuring that only ONE thread can call __cds_wfs_pop_blocking()
+ *    and __cds_wfs_pop_all(). (multi-provider/single-consumer scheme).
+ *
+ * "state" saves state flags atomically sampled with pop operation.
+ */
+static inline
+struct cds_wfs_node *
+___cds_wfs_pop_with_state_blocking(cds_wfs_stack_ptr_t u_stack, int *state)
+{
+	return ___cds_wfs_pop(u_stack, state, 1);
+}
+
+static inline
+struct cds_wfs_node *
+___cds_wfs_pop_blocking(cds_wfs_stack_ptr_t u_stack)
+{
+	return ___cds_wfs_pop_with_state_blocking(u_stack, NULL);
+}
+
+/*
+ * __cds_wfs_pop_with_state_nonblocking: pop a node from the stack.
+ *
+ * Same as __cds_wfs_pop_with_state_blocking, but returns
+ * CDS_WFS_WOULDBLOCK if it needs to block.
+ *
+ * "state" saves state flags atomically sampled with pop operation.
+ */
+static inline
+struct cds_wfs_node *
+___cds_wfs_pop_with_state_nonblocking(cds_wfs_stack_ptr_t u_stack, int *state)
+{
+	return ___cds_wfs_pop(u_stack, state, 0);
+}
+
+/*
+ * __cds_wfs_pop_nonblocking: pop a node from the stack.
+ *
+ * Same as __cds_wfs_pop_blocking, but returns CDS_WFS_WOULDBLOCK if
+ * it needs to block.
+ */
+static inline
+struct cds_wfs_node *
+___cds_wfs_pop_nonblocking(cds_wfs_stack_ptr_t u_stack)
+{
+	return ___cds_wfs_pop_with_state_nonblocking(u_stack, NULL);
+}
+
+/*
+ * __cds_wfs_pop_all: pop all nodes from a stack.
+ *
+ * __cds_wfs_pop_all does not require any synchronization with other
+ * push, nor with other __cds_wfs_pop_all, but requires synchronization
+ * matching the technique used to synchronize __cds_wfs_pop_blocking:
+ *
+ * 1) If __cds_wfs_pop_blocking is called under rcu read lock critical
+ *    section, both __cds_wfs_pop_blocking and cds_wfs_pop_all callers
+ *    must wait for a grace period to pass before freeing the returned
+ *    node or modifying the cds_wfs_node structure. However, no RCU
+ *    read-side critical section is needed around __cds_wfs_pop_all.
+ * 2) Using mutual exclusion (e.g. mutexes) to protect
+ *     __cds_wfs_pop_blocking and __cds_wfs_pop_all callers.
+ * 3) Ensuring that only ONE thread can call __cds_wfs_pop_blocking()
+ *    and __cds_wfs_pop_all(). (multi-provider/single-consumer scheme).
+ */
+static inline
+struct cds_wfs_head *
+___cds_wfs_pop_all(cds_wfs_stack_ptr_t u_stack)
+{
+	struct __cds_wfs_stack *s = u_stack._s;
+	struct cds_wfs_head *head;
+
+	/*
+	 * Implicit memory barrier after uatomic_xchg() matches implicit
+	 * memory barrier before uatomic_xchg() in cds_wfs_push. It
+	 * ensures that all nodes of the returned list are consistent.
+	 * There is no need to issue memory barriers when iterating on
+	 * the returned list, because the full memory barrier issued
+	 * prior to each uatomic_cmpxchg, which each write to head, are
+	 * taking care to order writes to each node prior to the full
+	 * memory barrier after this uatomic_xchg().
+	 */
+	head = uatomic_xchg(&s->head, CDS_WFS_END);
+	if (___cds_wfs_end(head))
+		return NULL;
+	return head;
+}
+
+/*
+ * cds_wfs_pop_lock: lock stack pop-protection mutex.
+ */
+static inline void _cds_wfs_pop_lock(struct cds_wfs_stack *s)
+{
+	int ret;
+
+	ret = pthread_mutex_lock(&s->lock);
+	assert(!ret);
+}
+
+/*
+ * cds_wfs_pop_unlock: unlock stack pop-protection mutex.
+ */
+static inline void _cds_wfs_pop_unlock(struct cds_wfs_stack *s)
+{
+	int ret;
+
+	ret = pthread_mutex_unlock(&s->lock);
+	assert(!ret);
+}
+
+/*
+ * Call __cds_wfs_pop_with_state_blocking with an internal pop mutex held.
+ */
+static inline
+struct cds_wfs_node *
+_cds_wfs_pop_with_state_blocking(struct cds_wfs_stack *s, int *state)
+{
+	struct cds_wfs_node *retnode;
+
+	_cds_wfs_pop_lock(s);
+	retnode = ___cds_wfs_pop_with_state_blocking(s, state);
+	_cds_wfs_pop_unlock(s);
+	return retnode;
+}
+
+/*
+ * Call _cds_wfs_pop_with_state_blocking without saving any state.
+ */
+static inline
+struct cds_wfs_node *
+_cds_wfs_pop_blocking(struct cds_wfs_stack *s)
+{
+	return _cds_wfs_pop_with_state_blocking(s, NULL);
+}
+
+/*
+ * Call __cds_wfs_pop_all with an internal pop mutex held.
+ */
+static inline
+struct cds_wfs_head *
+_cds_wfs_pop_all_blocking(struct cds_wfs_stack *s)
+{
+	struct cds_wfs_head *rethead;
+
+	_cds_wfs_pop_lock(s);
+	rethead = ___cds_wfs_pop_all(s);
+	_cds_wfs_pop_unlock(s);
+	return rethead;
+}
+
+/*
+ * cds_wfs_first: get first node of a popped stack.
+ *
+ * Content written into the node before enqueue is guaranteed to be
+ * consistent, but no other memory ordering is ensured.
+ *
+ * Used by for-like iteration macros in urcu/wfstack.h:
+ * cds_wfs_for_each_blocking()
+ * cds_wfs_for_each_blocking_safe()
+ *
+ * Returns NULL if popped stack is empty, top stack node otherwise.
+ */
+static inline struct cds_wfs_node *
+_cds_wfs_first(struct cds_wfs_head *head)
+{
+	if (___cds_wfs_end(head))
+		return NULL;
+	return &head->node;
+}
+
+static inline struct cds_wfs_node *
+___cds_wfs_next(struct cds_wfs_node *node, int blocking)
+{
+	struct cds_wfs_node *next;
+
+	next = ___cds_wfs_node_sync_next(node, blocking);
+	/*
+	 * CDS_WFS_WOULDBLOCK != CSD_WFS_END, so we can check for end
+	 * even if ___cds_wfs_node_sync_next returns CDS_WFS_WOULDBLOCK,
+	 * and still return CDS_WFS_WOULDBLOCK.
+	 */
+	if (___cds_wfs_end(next))
+		return NULL;
+	return next;
+}
+
+/*
+ * cds_wfs_next_blocking: get next node of a popped stack.
+ *
+ * Content written into the node before enqueue is guaranteed to be
+ * consistent, but no other memory ordering is ensured.
+ *
+ * Used by for-like iteration macros in urcu/wfstack.h:
+ * cds_wfs_for_each_blocking()
+ * cds_wfs_for_each_blocking_safe()
+ *
+ * Returns NULL if reached end of popped stack, non-NULL next stack
+ * node otherwise.
+ */
+static inline struct cds_wfs_node *
+_cds_wfs_next_blocking(struct cds_wfs_node *node)
+{
+	return ___cds_wfs_next(node, 1);
+}
+
+
+/*
+ * cds_wfs_next_nonblocking: get next node of a popped stack.
+ *
+ * Same as cds_wfs_next_blocking, but returns CDS_WFS_WOULDBLOCK if it
+ * needs to block.
+ */
+static inline struct cds_wfs_node *
+_cds_wfs_next_nonblocking(struct cds_wfs_node *node)
+{
+	return ___cds_wfs_next(node, 0);
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _URCU_STATIC_WFSTACK_H */