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Commit 7cb45c0f authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

locking/barriers: Move smp_cond_load_acquire() to asm-generic/barrier.h 



Since all asm/barrier.h should/must include asm-generic/barrier.h the
latter is a good place for generic infrastructure like this.

This also allows archs to override the new smp_acquire__after_ctrl_dep().

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 33ac2796

include/asm-generic/barrier.h

+39 −0
Original line number Diff line number Diff line
@@ -207,5 +207,44 @@ do { \ 
#define virt_store_release(p, v) __smp_store_release(p, v)

#define virt_load_acquire(p) __smp_load_acquire(p)



/**

 * smp_acquire__after_ctrl_dep() - Provide ACQUIRE ordering after a control dependency

 *

 * A control dependency provides a LOAD->STORE order, the additional RMB

 * provides LOAD->LOAD order, together they provide LOAD->{LOAD,STORE} order,

 * aka. (load)-ACQUIRE.

 *

 * Architectures that do not do load speculation can have this be barrier().

 */

#ifndef smp_acquire__after_ctrl_dep

#define smp_acquire__after_ctrl_dep()		smp_rmb()

#endif



/**

 * smp_cond_load_acquire() - (Spin) wait for cond with ACQUIRE ordering

 * @ptr: pointer to the variable to wait on

 * @cond: boolean expression to wait for

 *

 * Equivalent to using smp_load_acquire() on the condition variable but employs

 * the control dependency of the wait to reduce the barrier on many platforms.

 *

 * Due to C lacking lambda expressions we load the value of *ptr into a

 * pre-named variable @VAL to be used in @cond.

 */

#ifndef smp_cond_load_acquire

#define smp_cond_load_acquire(ptr, cond_expr) ({		\

	typeof(ptr) __PTR = (ptr);				\

	typeof(*ptr) VAL;					\

	for (;;) {						\

		VAL = READ_ONCE(*__PTR);			\

		if (cond_expr)					\

			break;					\

		cpu_relax();					\

	}							\

	smp_acquire__after_ctrl_dep();				\

	VAL;							\

})

#endif



#endif /* !__ASSEMBLY__ */

#endif /* __ASM_GENERIC_BARRIER_H */

include/linux/compiler.h

+0 −37
Original line number Diff line number Diff line
@@ -304,43 +304,6 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s 
	__u.__val;					\

})



/**

 * smp_acquire__after_ctrl_dep() - Provide ACQUIRE ordering after a control dependency

 *

 * A control dependency provides a LOAD->STORE order, the additional RMB

 * provides LOAD->LOAD order, together they provide LOAD->{LOAD,STORE} order,

 * aka. (load)-ACQUIRE.

 *

 * Architectures that do not do load speculation can have this be barrier().

 */

#define smp_acquire__after_ctrl_dep()		smp_rmb()



/**

 * smp_cond_load_acquire() - (Spin) wait for cond with ACQUIRE ordering

 * @ptr: pointer to the variable to wait on

 * @cond: boolean expression to wait for

 *

 * Equivalent to using smp_load_acquire() on the condition variable but employs

 * the control dependency of the wait to reduce the barrier on many platforms.

 *

 * Due to C lacking lambda expressions we load the value of *ptr into a

 * pre-named variable @VAL to be used in @cond.

 */

#ifndef smp_cond_load_acquire

#define smp_cond_load_acquire(ptr, cond_expr) ({		\

	typeof(ptr) __PTR = (ptr);				\

	typeof(*ptr) VAL;					\

	for (;;) {						\

		VAL = READ_ONCE(*__PTR);			\

		if (cond_expr)					\

			break;					\

		cpu_relax();					\

	}							\

	smp_acquire__after_ctrl_dep();				\

	VAL;							\

})

#endif



#endif /* __KERNEL__ */



#endif /* __ASSEMBLY__ */