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Date: Fri, 15 Nov 2013 16:40:17 -0800
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com,
edumazet@...gle.com, darren@...art.com, fweisbec@...il.com,
sbw@....edu, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 14/14] rcu: Add an RCU_INITIALIZER for global RCU-protected pointers
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
There is currently no way to initialize a global RCU-protected pointer
without either putting up with sparse complaints or open-coding an
obscure cast. This commit therefore creates RCU_INITIALIZER(), which
is intended to be used as follows:
struct foo __rcu *p = RCU_INITIALIZER(&my_rcu_structure);
This commit also applies RCU_INITIALIZER() to eliminate repeated
open-coded obscure casts in __rcu_assign_pointer(), RCU_INIT_POINTER(),
and RCU_POINTER_INITIALIZER(). This commit also inlines
__rcu_assign_pointer() into its only caller, rcu_assign_pointer().
Suggested-by: Steven Rostedt <rostedt@...dmis.org>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
include/linux/rcupdate.h | 80 +++++++++++++++++++++++++-----------------------
1 file changed, 42 insertions(+), 38 deletions(-)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 08c961fa7699..cebe555c06ce 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -557,11 +557,49 @@ static inline void rcu_preempt_sleep_check(void)
smp_read_barrier_depends(); \
(_________p1); \
})
-#define __rcu_assign_pointer(p, v, space) \
+
+/**
+ * RCU_INITIALIZER() - statically initialize an RCU-protected global variable
+ * @v: The value to statically initialize with.
+ */
+#define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v)
+
+/**
+ * rcu_assign_pointer() - assign to RCU-protected pointer
+ * @p: pointer to assign to
+ * @v: value to assign (publish)
+ *
+ * Assigns the specified value to the specified RCU-protected
+ * pointer, ensuring that any concurrent RCU readers will see
+ * any prior initialization.
+ *
+ * Inserts memory barriers on architectures that require them
+ * (which is most of them), and also prevents the compiler from
+ * reordering the code that initializes the structure after the pointer
+ * assignment. More importantly, this call documents which pointers
+ * will be dereferenced by RCU read-side code.
+ *
+ * In some special cases, you may use RCU_INIT_POINTER() instead
+ * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due
+ * to the fact that it does not constrain either the CPU or the compiler.
+ * That said, using RCU_INIT_POINTER() when you should have used
+ * rcu_assign_pointer() is a very bad thing that results in
+ * impossible-to-diagnose memory corruption. So please be careful.
+ * See the RCU_INIT_POINTER() comment header for details.
+ *
+ * Note that rcu_assign_pointer() evaluates each of its arguments only
+ * once, appearances notwithstanding. One of the "extra" evaluations
+ * is in typeof() and the other visible only to sparse (__CHECKER__),
+ * neither of which actually execute the argument. As with most cpp
+ * macros, this execute-arguments-only-once property is important, so
+ * please be careful when making changes to rcu_assign_pointer() and the
+ * other macros that it invokes.
+ */
+#define rcu_assign_pointer(p, v) \
do { \
smp_wmb(); \
__rcu_assign_pointer_check_kernel(v); \
- ACCESS_ONCE(p) = (typeof(*(v)) __force space *)(v); \
+ ACCESS_ONCE(p) = RCU_INITIALIZER(v); \
} while (0)
@@ -900,40 +938,6 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
}
/**
- * rcu_assign_pointer() - assign to RCU-protected pointer
- * @p: pointer to assign to
- * @v: value to assign (publish)
- *
- * Assigns the specified value to the specified RCU-protected
- * pointer, ensuring that any concurrent RCU readers will see
- * any prior initialization.
- *
- * Inserts memory barriers on architectures that require them
- * (which is most of them), and also prevents the compiler from
- * reordering the code that initializes the structure after the pointer
- * assignment. More importantly, this call documents which pointers
- * will be dereferenced by RCU read-side code.
- *
- * In some special cases, you may use RCU_INIT_POINTER() instead
- * of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due
- * to the fact that it does not constrain either the CPU or the compiler.
- * That said, using RCU_INIT_POINTER() when you should have used
- * rcu_assign_pointer() is a very bad thing that results in
- * impossible-to-diagnose memory corruption. So please be careful.
- * See the RCU_INIT_POINTER() comment header for details.
- *
- * Note that rcu_assign_pointer() evaluates each of its arguments only
- * once, appearances notwithstanding. One of the "extra" evaluations
- * is in typeof() and the other visible only to sparse (__CHECKER__),
- * neither of which actually execute the argument. As with most cpp
- * macros, this execute-arguments-only-once property is important, so
- * please be careful when making changes to rcu_assign_pointer() and the
- * other macros that it invokes.
- */
-#define rcu_assign_pointer(p, v) \
- __rcu_assign_pointer((p), (v), __rcu)
-
-/**
* RCU_INIT_POINTER() - initialize an RCU protected pointer
*
* Initialize an RCU-protected pointer in special cases where readers
@@ -967,7 +971,7 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
*/
#define RCU_INIT_POINTER(p, v) \
do { \
- p = (typeof(*v) __force __rcu *)(v); \
+ p = RCU_INITIALIZER(v); \
} while (0)
/**
@@ -976,7 +980,7 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
* GCC-style initialization for an RCU-protected pointer in a structure field.
*/
#define RCU_POINTER_INITIALIZER(p, v) \
- .p = (typeof(*v) __force __rcu *)(v)
+ .p = RCU_INITIALIZER(v)
/*
* Does the specified offset indicate that the corresponding rcu_head
--
1.8.1.5
--
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