include/wrapper/barrier.h

   1 /* SPDX-License-Identifier: GPL-2.0-only
   2  *
   3  * wrapper/barrier.h
   4  *
   5  * wrapper around asm/barrier.h.
   6  *
   7  * Copyright (C) 2020 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   8  */
   9
  10 #ifndef _LTTNG_WRAPPER_BARRIER_H
  11 #define _LTTNG_WRAPPER_BARRIER_H
  12
  13 #include <linux/version.h>
  14 #include <asm/barrier.h>
  15
  16 #if LINUX_VERSION_CODE >= KERNEL_VERSION(3,14,0)
  17
  18 #define lttng_smp_store_release(x, v) smp_store_release(x, v)
  19 #define lttng_smp_load_acquire(x) smp_load_acquire(x)
  20
  21 #else
  22
  23 /*
  24  * Acquire-release semantics act as a one-way permeable barrier when
  25  * pairing a store with a release. Use a full memory barrier to emulate
  26  * the acquire-release semantic with a stronger barrier on older
  27  * kernels.
  28  */
  29
  30 #define lttng_smp_store_release(x, v)           \
  31         do {                                    \
  32                 smp_mb();                       \
  33                 ACCESS_ONCE(*(x)) = (v);        \
  34         } while (0)
  35
  36 #define lttng_smp_load_acquire(x)               \
  37         ({                                      \
  38                 __typeof__(*(x)) ___ret;        \
  39                                                 \
  40                 ___ret = ACCESS_ONCE(*(x));     \
  41                 smp_mb();                       \
  42                 ___ret;                         \
  43         })
  44
  45 #endif
  46
  47 #endif /* _LTTNG_WRAPPER_BARRIER_H */