diff options
Diffstat (limited to 'include/linux/compiler.h')
| -rw-r--r-- | include/linux/compiler.h | 25 |
1 files changed, 19 insertions, 6 deletions
diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 06f27fd9d760..2bcaedc0f032 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -305,21 +305,34 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s }) /** - * smp_cond_acquire() - Spin wait for cond with ACQUIRE ordering + * 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. + * * The control dependency provides a LOAD->STORE order, the additional RMB * provides LOAD->LOAD order, together they provide LOAD->{LOAD,STORE} order, * aka. ACQUIRE. */ -#define smp_cond_acquire(cond) do { \ - while (!(cond)) \ - cpu_relax(); \ - smp_rmb(); /* ctrl + rmb := acquire */ \ -} while (0) +#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_rmb(); /* ctrl + rmb := acquire */ \ + VAL; \ +}) +#endif #endif /* __KERNEL__ */ |