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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-10-27 21:11:27 -0700
committerAl Viro <viro@zeniv.linux.org.uk>2014-10-28 18:25:17 -0400
commit54ef6df3f3f1353d99c80c437259d317b2cd1cbd (patch)
tree22b1c691757577cb291430858def7d86d8449dfb
parent5fecf3a1e1a0af61eb34eb6976ec9f59cca65d3f (diff)
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>
-rw-r--r--include/linux/rcupdate.h15
1 files changed, 15 insertions, 0 deletions
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index a4a819ffb2d1..53ff1a752d7e 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -617,6 +617,21 @@ 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
* @v: value to assign (publish)