1 files changed, 52 insertions, 0 deletions

diff --git a/include/linux/percpu.h b/include/linux/percpu.h
index ee5615d65211..cfda2d5ad319 100644
--- a/include/linux/percpu.h
+++ b/include/linux/percpu.h
@@ -168,4 +168,56 @@ static inline void free_percpu(void *p)
 #define alloc_percpu(type)      (type *)__alloc_percpu(sizeof(type), \
                                                        __alignof__(type))
 
+/*
+ * Optional methods for optimized non-lvalue per-cpu variable access.
+ *
+ * @var can be a percpu variable or a field of it and its size should
+ * equal char, int or long.  percpu_read() evaluates to a lvalue and
+ * all others to void.
+ *
+ * These operations are guaranteed to be atomic w.r.t. preemption.
+ * The generic versions use plain get/put_cpu_var().  Archs are
+ * encouraged to implement single-instruction alternatives which don't
+ * require preemption protection.
+ */
+#ifndef percpu_read
+# define percpu_read(var)                                               \
+  ({                                                                    \
+        typeof(per_cpu_var(var)) __tmp_var__;                           \
+        __tmp_var__ = get_cpu_var(var);                                 \
+        put_cpu_var(var);                                               \
+        __tmp_var__;                                                    \
+  })
+#endif
+
+#define __percpu_generic_to_op(var, val, op)                            \
+do {                                                                    \
+        get_cpu_var(var) op val;                                        \
+        put_cpu_var(var);                                               \
+} while (0)
+
+#ifndef percpu_write
+# define percpu_write(var, val)         __percpu_generic_to_op(var, (val), =)
+#endif
+
+#ifndef percpu_add
+# define percpu_add(var, val)           __percpu_generic_to_op(var, (val), +=)
+#endif
+
+#ifndef percpu_sub
+# define percpu_sub(var, val)           __percpu_generic_to_op(var, (val), -=)
+#endif
+
+#ifndef percpu_and
+# define percpu_and(var, val)           __percpu_generic_to_op(var, (val), &=)
+#endif
+
+#ifndef percpu_or
+# define percpu_or(var, val)            __percpu_generic_to_op(var, (val), |=)
+#endif
+
+#ifndef percpu_xor
+# define percpu_xor(var, val)           __percpu_generic_to_op(var, (val), ^=)
+#endif
+
 #endif /* __LINUX_PERCPU_H */