1 files changed, 16 insertions, 0 deletions

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 03e227ba481c..05be2352fef8 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -252,6 +252,22 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
 #define WRITE_ONCE(x, val) \
         ({ union { typeof(x) __val; char __c[1]; } __u = { .__val = (val) }; __write_once_size(&(x), __u.__c, sizeof(x)); __u.__val; })
 
+/**
+ * READ_ONCE_CTRL - Read a value heading a control dependency
+ * @x: The value to be read, heading the control dependency
+ *
+ * Control dependencies are tricky.  See Documentation/memory-barriers.txt
+ * for important information on how to use them.  Note that in many cases,
+ * use of smp_load_acquire() will be much simpler.  Control dependencies
+ * should be avoided except on the hottest of hotpaths.
+ */
+#define READ_ONCE_CTRL(x) \
+({ \
+        typeof(x) __val = READ_ONCE(x); \
+        smp_read_barrier_depends(); /* Enforce control dependency. */ \
+        __val; \
+})
+
 #endif /* __KERNEL__ */
 
 #endif /* __ASSEMBLY__ */