rcu: merge fix for Convert ACCESS_ONCE() to READ_ONCE() and WRITE_ONCE()

[karo-tx-linux.git] / include / linux / compiler.h

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 867722591be2c7e026e1b97c241e65e27e3b9d1b..52bdec710ed7ebb270fa3fbae247c8650ed15571 100644 (file)
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -457,6 +457,21 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
        (volatile typeof(x) *)&(x); })
 #define ACCESS_ONCE(x) (*__ACCESS_ONCE(x))
 
+/**
+ * lockless_dereference() - safely load a pointer for later dereference
+ * @p: The pointer to load
+ *
+ * Similar to rcu_dereference(), but for situations where the pointed-to
+ * object's lifetime is managed by something other than RCU.  That
+ * "something other" might be reference counting or simple immortality.
+ */
+#define lockless_dereference(p) \
+({ \
+       typeof(p) _________p1 = READ_ONCE(p); \
+       smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
+       (_________p1); \
+})
+
 /* Ignore/forbid kprobes attach on very low level functions marked by this attribute: */
 #ifdef CONFIG_KPROBES
 # define __kprobes     __attribute__((__section__(".kprobes.text")))