+/*
+ * Using a two-subphases algorithm for architectures with smaller than 64-bit
+ * long-size to ensure we do not encounter an overflow bug.
+ */
+
+#if (BITS_PER_LONG < 64)
+/*
+ * called with urcu_mutex held.
+ */
+static void switch_next_urcu_qparity(void)
+{
+ STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR);
+}
+
+void synchronize_rcu(void)
+{
+ /* All threads should read qparity before accessing data structure
+ * where new ptr points to.
+ */
+ /* Write new ptr before changing the qparity */
+ smp_mb();
+
+ internal_urcu_lock();
+
+ switch_next_urcu_qparity(); /* 0 -> 1 */
+
+ /*
+ * Must commit qparity update to memory before waiting for parity
+ * 0 quiescent state. Failure to do so could result in the writer
+ * waiting forever while new readers are always accessing data (no
+ * progress).
+ * Ensured by STORE_SHARED and LOAD_SHARED.
+ */
+
+ /*
+ * Wait for previous parity to be empty of readers.
+ */
+ wait_for_quiescent_state(); /* Wait readers in parity 0 */
+
+ /*
+ * Must finish waiting for quiescent state for parity 0 before
+ * committing qparity update to memory. Failure to do so could result in
+ * the writer waiting forever while new readers are always accessing
+ * data (no progress).
+ * Ensured by STORE_SHARED and LOAD_SHARED.
+ */
+
+ switch_next_urcu_qparity(); /* 1 -> 0 */
+
+ /*
+ * Must commit qparity update to memory before waiting for parity
+ * 1 quiescent state. Failure to do so could result in the writer
+ * waiting forever while new readers are always accessing data (no
+ * progress).
+ * Ensured by STORE_SHARED and LOAD_SHARED.
+ */
+
+ /*
+ * Wait for previous parity to be empty of readers.
+ */
+ wait_for_quiescent_state(); /* Wait readers in parity 1 */
+
+ internal_urcu_unlock();
+
+ /* Finish waiting for reader threads before letting the old ptr being
+ * freed.
+ */
+ smp_mb();
+}
+#else /* !(BITS_PER_LONG < 64) */