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Commit 462225ae authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Add an RCU_INITIALIZER for global RCU-protected pointers 



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: default avatarSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: default avatarJosh Triplett <josh@joshtriplett.org>
parent 9d162cd0

include/linux/rcupdate.h

+42 −38
Original line number Diff line number Diff line
@@ -548,10 +548,48 @@ 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(); \

		ACCESS_ONCE(p) = (typeof(*(v)) __force space *)(v); \

		ACCESS_ONCE(p) = RCU_INITIALIZER(v); \

	} while (0)
@@ -889,40 +927,6 @@ static inline notrace void rcu_read_unlock_sched_notrace(void) 
	preempt_enable_notrace();

}



/**

 * 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

 *
@@ -957,7 +961,7 @@ 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)



/**
@@ -966,7 +970,7 @@ 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