From 54ef6df3f3f1353d99c80c437259d317b2cd1cbd Mon Sep 17 00:00:00 2001
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Date: Mon, 27 Oct 2014 21:11:27 -0700
Subject: [PATCH] rcu: Provide counterpart to rcu_dereference() for non-RCU
situations
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@ZenIV.linux.org.uk>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
include/linux/rcupdate.h | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index a4a819ffb2d11..53ff1a752d7e2 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -616,6 +616,21 @@ static inline void rcu_preempt_sleep_check(void)
*/
#define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
+/**
+ * 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_assign_pointer() - assign to RCU-protected pointer
* @p: pointer to assign to
--
2.30.2