[PATCH 3.12 61/82] rcu: Provide counterpart to rcu_dereference() for non-RCU situations
From: "Paul E. McKenney"
3.12-stable review patch. If anyone has any objections, please let me 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
Signed-off-by: Paul E. McKenney
Signed-off-by: Al Viro
Signed-off-by: Jiri Slaby
---
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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[PATCH 3.12 61/82] rcu: Provide counterpart to rcu_dereference() for non-RCU situations
From: Paul E. McKenney paul...@linux.vnet.ibm.com
3.12-stable review patch. If anyone has any objections, please let me 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 v...@zeniv.linux.org.uk
Signed-off-by: Paul E. McKenney paul...@linux.vnet.ibm.com
Signed-off-by: Al Viro v...@zeniv.linux.org.uk
Signed-off-by: Jiri Slaby jsl...@suse.cz
---
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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