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 #if LINUX_VERSION_CODE >= KERNEL_VERSION(3,4,0)
  15 #include <asm/barrier.h>
  16 #else
  17 #include <asm/system.h>
  18 #endif
  19
  20 #if LINUX_VERSION_CODE >= KERNEL_VERSION(3,14,0)
  21
  22 #define lttng_smp_store_release(x, v) smp_store_release(x, v)
  23 #define lttng_smp_load_acquire(x) smp_load_acquire(x)
  24
  25 #else
  26
  27 /*
  28  * Acquire-release semantics act as a one-way permeable barrier when
  29  * pairing a store with a release. Use a full memory barrier to emulate
  30  * the acquire-release semantic with a stronger barrier on older
  31  * kernels.
  32  */
  33
  34 #define lttng_smp_store_release(x, v)           \
  35         do {                                    \
  36                 smp_mb();                       \
  37                 ACCESS_ONCE(*(x)) = (v);        \
  38         } while (0)
  39
  40 #define lttng_smp_load_acquire(x)               \
  41         ({                                      \
  42                 __typeof__(*(x)) ___ret;        \
  43                                                 \
  44                 ___ret = ACCESS_ONCE(*(x));     \
  45                 smp_mb();                       \
  46                 ___ret;                         \
  47         })
  48
  49 #endif
  50
  51 #endif /* _LTTNG_WRAPPER_BARRIER_H */