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locking/barriers: Introduce smp_acquire__after_ctrl_dep()

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Introduce smp_acquire__after_ctrl_dep(), this construct is not
uncommon, but the lack of this barrier is.

Use it to better express smp_rmb() uses in WRITE_ONCE(), the IPC
semaphore code and the qspinlock code.

Signed-off-by: Peter 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>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2016-05-24 13:17:12 +02:00 • committed by Ingo Molnar
parent 1f03e8d291
commit 33ac279677
3 changed files with 15 additions and 18 deletions
Download patch file Download diff file Expand all files Collapse all files

17
include/linux/compiler.h
View file

@ -304,6 +304,17 @@ 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
@ -314,10 +325,6 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
*
* Due to C lacking lambda expressions we load the value of *ptr into a
* pre-named variable @VAL to be used in @cond.
*
* The control dependency provides a LOAD->STORE order, the additional RMB
* provides LOAD->LOAD order, together they provide LOAD->{LOAD,STORE} order,
* aka. ACQUIRE.
*/
#ifndef smp_cond_load_acquire
#define smp_cond_load_acquire(ptr, cond_expr) ({ \
@ -329,7 +336,7 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
break; \
cpu_relax(); \
} \
smp_rmb(); /* ctrl + rmb := acquire */ \
smp_acquire__after_ctrl_dep(); \
VAL; \
})
#endif