+/*
+ * reading current mems_allowed and mempolicy in the fastpath must protected
+ * by get_mems_allowed()
+ */
+static inline void get_mems_allowed(void)
+{
+ current->mems_allowed_change_disable++;
+
+ /*
+ * ensure that reading mems_allowed and mempolicy happens after the
+ * update of ->mems_allowed_change_disable.
+ *
+ * the write-side task finds ->mems_allowed_change_disable is not 0,
+ * and knows the read-side task is reading mems_allowed or mempolicy,
+ * so it will clear old bits lazily.
+ */
+ smp_mb();
+}
+
+static inline void put_mems_allowed(void)
+{
+ /*
+ * ensure that reading mems_allowed and mempolicy before reducing
+ * mems_allowed_change_disable.
+ *
+ * the write-side task will know that the read-side task is still
+ * reading mems_allowed or mempolicy, don't clears old bits in the
+ * nodemask.
+ */
+ smp_mb();
+ --ACCESS_ONCE(current->mems_allowed_change_disable);
+}
+