diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2016-05-24 13:17:12 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2016-06-14 11:55:14 +0200 |
| commit | 33ac279677dcc2441cb93d8cb9cf7a74df62814d (patch) | |
| tree | bcf918587b2425d1294b780b31ab67761e068e26 /include | |
| parent | 1f03e8d2919270bd6ef64f39a45ce8df8a9f012a (diff) | |
| download | lwn-33ac279677dcc2441cb93d8cb9cf7a74df62814d.tar.gz lwn-33ac279677dcc2441cb93d8cb9cf7a74df62814d.zip | |
locking/barriers: Introduce smp_acquire__after_ctrl_dep()
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>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/compiler.h | 17 |
1 files changed, 12 insertions, 5 deletions
diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 2bcaedc0f032..59a7004fc7dd 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -305,6 +305,17 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s }) /** + * 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 @@ -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 |