include/linux/atomic.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /* Atomic operations usable in machine independent code */
   3 #ifndef _LINUX_ATOMIC_H
   4 #define _LINUX_ATOMIC_H
   5 #include <linux/types.h>
   6
   7 #include <asm/atomic.h>
   8 #include <asm/barrier.h>
   9
  10 /*
  11  * Relaxed variants of xchg, cmpxchg and some atomic operations.
  12  *
  13  * We support four variants:
  14  *
  15  * - Fully ordered: The default implementation, no suffix required.
  16  * - Acquire: Provides ACQUIRE semantics, _acquire suffix.
  17  * - Release: Provides RELEASE semantics, _release suffix.
  18  * - Relaxed: No ordering guarantees, _relaxed suffix.
  19  *
  20  * For compound atomics performing both a load and a store, ACQUIRE
  21  * semantics apply only to the load and RELEASE semantics only to the
  22  * store portion of the operation. Note that a failed cmpxchg_acquire
  23  * does -not- imply any memory ordering constraints.
  24  *
  25  * See Documentation/memory-barriers.txt for ACQUIRE/RELEASE definitions.
  26  */
  27
  28 /*
  29  * The idea here is to build acquire/release variants by adding explicit
  30  * barriers on top of the relaxed variant. In the case where the relaxed
  31  * variant is already fully ordered, no additional barriers are needed.
  32  *
  33  * If an architecture overrides __atomic_acquire_fence() it will probably
  34  * want to define smp_mb__after_spinlock().
  35  */
  36 #ifndef __atomic_acquire_fence
  37 #define __atomic_acquire_fence          smp_mb__after_atomic
  38 #endif
  39
  40 #ifndef __atomic_release_fence
  41 #define __atomic_release_fence          smp_mb__before_atomic
  42 #endif
  43
  44 #ifndef __atomic_pre_full_fence
  45 #define __atomic_pre_full_fence         smp_mb__before_atomic
  46 #endif
  47
  48 #ifndef __atomic_post_full_fence
  49 #define __atomic_post_full_fence        smp_mb__after_atomic
  50 #endif
  51
  52 #define __atomic_op_acquire(op, args...)                                \
  53 ({                                                                      \
  54         typeof(op##_relaxed(args)) __ret  = op##_relaxed(args);         \
  55         __atomic_acquire_fence();                                       \
  56         __ret;                                                          \
  57 })
  58
  59 #define __atomic_op_release(op, args...)                                \
  60 ({                                                                      \
  61         __atomic_release_fence();                                       \
  62         op##_relaxed(args);                                             \
  63 })
  64
  65 #define __atomic_op_fence(op, args...)                                  \
  66 ({                                                                      \
  67         typeof(op##_relaxed(args)) __ret;                               \
  68         __atomic_pre_full_fence();                                      \
  69         __ret = op##_relaxed(args);                                     \
  70         __atomic_post_full_fence();                                     \
  71         __ret;                                                          \
  72 })
  73
  74 #include <linux/atomic-fallback.h>
  75
  76 #include <asm-generic/atomic-long.h>
  77
  78 #endif /* _LINUX_ATOMIC_H */