Introduce lttng smp_store_release smp_load_acquire wrappers

[lttng-modules.git] / include / wrapper / barrier.h

diff --git a/include/wrapper/barrier.h b/include/wrapper/barrier.h
new file mode 100644 (file)
index 0000000..c2f0545
--- /dev/null
+++ b/include/wrapper/barrier.h
@@ -0,0 +1,47 @@
+/* SPDX-License-Identifier: GPL-2.0-only
+ *
+ * wrapper/barrier.h
+ *
+ * wrapper around asm/barrier.h.
+ *
+ * Copyright (C) 2020 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ */
+
+#ifndef _LTTNG_WRAPPER_BARRIER_H
+#define _LTTNG_WRAPPER_BARRIER_H
+
+#include <linux/version.h>
+#include <asm/barrier.h>
+
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(3,14,0)
+
+#define lttng_smp_store_release(x, v) smp_store_release(x, v)
+#define lttng_smp_load_acquire(x) smp_load_acquire(x)
+
+#else
+
+/*
+ * Acquire-release semantics act as a one-way permeable barrier when
+ * pairing a store with a release. Use a full memory barrier to emulate
+ * the acquire-release semantic with a stronger barrier on older
+ * kernels.
+ */
+
+#define lttng_smp_store_release(x, v)          \
+       do {                                    \
+               smp_mb();                       \
+               ACCESS_ONCE(*(x)) = (v);        \
+       } while (0)
+
+#define lttng_smp_load_acquire(x)              \
+       ({                                      \
+               __typeof__(*(x)) ___ret;        \
+                                               \
+               ___ret = ACCESS_ONCE(*(x));     \
+               smp_mb();                       \
+               ___ret;                         \
+       })
+
+#endif
+
+#endif /* _LTTNG_WRAPPER_BARRIER_H */