From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
This patch has been added to the 3.12 stable tree. If you have any
objections, please let us know.
===============
commit 54ef6df3f3f1353d99c80c437259d317b2cd1cbd upstream.
Although rcu_dereference() and friends can be used in situations where
object lifetimes are being managed by something other than RCU, the
resulting sparse and lockdep-RCU noise can be annoying. This commit
therefore supplies a lockless_dereference(), which provides the
protection for dereferences without the RCU-related debugging noise.
Reported-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
include/linux/rcupdate.h | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index f1f1bc39346b..4912c953cab7 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -554,6 +554,20 @@ static inline void rcu_preempt_sleep_check(void)
(p) = (typeof(*v) __force space *)(v); \
} while (0)
+/**
+ * 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 = ACCESS_ONCE(p); \
+ smp_read_barrier_depends(); /* Dependency order vs. p above. */ \
+ (_________p1); \
+})
/**
* rcu_access_pointer() - fetch RCU pointer with no dereferencing
--
2.5.0
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