include/urcu/static/urcu-mb.h

   1 // SPDX-FileCopyrightText: 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   2 // SPDX-FileCopyrightText: 2009 Paul E. McKenney, IBM Corporation.
   3 //
   4 // SPDX-License-Identifier: LGPL-2.1-or-later
   5
   6 #ifndef _URCU_MB_STATIC_H
   7 #define _URCU_MB_STATIC_H
   8
   9 /*
  10  * Userspace RCU header.
  11  *
  12  * TO BE INCLUDED ONLY IN CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU
  13  * RELEASE. See urcu.h for linking dynamically with the userspace rcu library.
  14  *
  15  * IBM's contributions to this file may be relicensed under LGPLv2 or later.
  16  */
  17
  18 #include <stdlib.h>
  19 #include <pthread.h>
  20 #include <unistd.h>
  21 #include <stdint.h>
  22
  23 #include <urcu/debug.h>
  24 #include <urcu/config.h>
  25 #include <urcu/compiler.h>
  26 #include <urcu/arch.h>
  27 #include <urcu/system.h>
  28 #include <urcu/uatomic.h>
  29 #include <urcu/list.h>
  30 #include <urcu/futex.h>
  31 #include <urcu/tls-compat.h>
  32 #include <urcu/static/urcu-common.h>
  33
  34 #ifdef __cplusplus
  35 extern "C" {
  36 #endif
  37
  38 /*
  39  * This code section can only be included in LGPL 2.1 compatible source code.
  40  * See below for the function call wrappers which can be used in code meant to
  41  * be only linked with the Userspace RCU library. This comes with a small
  42  * performance degradation on the read-side due to the added function calls.
  43  * This is required to permit relinking with newer versions of the library.
  44  */
  45
  46 extern struct urcu_gp urcu_mb_gp;
  47
  48 extern DECLARE_URCU_TLS(struct urcu_reader, urcu_mb_reader);
  49
  50 /*
  51  * Helper for _urcu_mb_read_lock().  The format of urcu_mb_gp.ctr (as well as
  52  * the per-thread rcu_reader.ctr) has the lower-order bits containing a count of
  53  * _urcu_mb_read_lock() nesting, and a single high-order URCU_BP_GP_CTR_PHASE bit
  54  * that contains either zero or one.  The cmm_smp_mb() ensures that the accesses in
  55  * _urcu_mb_read_lock() happen before the subsequent read-side critical section.
  56  */
  57 static inline void _urcu_mb_read_lock_update(unsigned long tmp)
  58 {
  59         if (caa_likely(!(tmp & URCU_GP_CTR_NEST_MASK))) {
  60                 _CMM_STORE_SHARED(URCU_TLS(urcu_mb_reader).ctr, _CMM_LOAD_SHARED(urcu_mb_gp.ctr));
  61                 cmm_smp_mb();
  62         } else
  63                 _CMM_STORE_SHARED(URCU_TLS(urcu_mb_reader).ctr, tmp + URCU_GP_COUNT);
  64 }
  65
  66 /*
  67  * Enter an RCU read-side critical section.
  68  *
  69  * The first cmm_barrier() call ensures that the compiler does not reorder
  70  * the body of _urcu_mb_read_lock() with a mutex.
  71  *
  72  * This function and its helper are both less than 10 lines long.  The
  73  * intent is that this function meets the 10-line criterion in LGPL,
  74  * allowing this function to be invoked directly from non-LGPL code.
  75  */
  76 static inline void _urcu_mb_read_lock(void)
  77 {
  78         unsigned long tmp;
  79
  80         urcu_assert_debug(URCU_TLS(urcu_mb_reader).registered);
  81         cmm_barrier();
  82         tmp = URCU_TLS(urcu_mb_reader).ctr;
  83         urcu_assert_debug((tmp & URCU_GP_CTR_NEST_MASK) != URCU_GP_CTR_NEST_MASK);
  84         _urcu_mb_read_lock_update(tmp);
  85 }
  86
  87 /*
  88  * This is a helper function for _urcu_mb_read_unlock().
  89  *
  90  * The first cmm_smp_mb() call ensures that the critical section is
  91  * seen to precede the store to rcu_reader.ctr.
  92  * The second cmm_smp_mb() call ensures that we write to rcu_reader.ctr
  93  * before reading the update-side futex.
  94  */
  95 static inline void _urcu_mb_read_unlock_update_and_wakeup(unsigned long tmp)
  96 {
  97         unsigned long *ctr = &URCU_TLS(urcu_mb_reader).ctr;
  98
  99         if (caa_likely((tmp & URCU_GP_CTR_NEST_MASK) == URCU_GP_COUNT)) {
 100                 uatomic_store(ctr, tmp - URCU_GP_COUNT, CMM_SEQ_CST);
 101                 urcu_common_wake_up_gp(&urcu_mb_gp);
 102         } else {
 103                 uatomic_store(ctr, tmp - URCU_GP_COUNT, CMM_RELAXED);
 104         }
 105 }
 106
 107 /*
 108  * Exit an RCU read-side critical section.  Both this function and its
 109  * helper are smaller than 10 lines of code, and are intended to be
 110  * usable by non-LGPL code, as called out in LGPL.
 111  */
 112 static inline void _urcu_mb_read_unlock(void)
 113 {
 114         unsigned long tmp;
 115
 116         urcu_assert_debug(URCU_TLS(urcu_mb_reader).registered);
 117         tmp = URCU_TLS(urcu_mb_reader).ctr;
 118         urcu_assert_debug(tmp & URCU_GP_CTR_NEST_MASK);
 119         _urcu_mb_read_unlock_update_and_wakeup(tmp);
 120         cmm_barrier();  /* Ensure the compiler does not reorder us with mutex */
 121 }
 122
 123 /*
 124  * Returns whether within a RCU read-side critical section.
 125  *
 126  * This function is less than 10 lines long.  The intent is that this
 127  * function meets the 10-line criterion for LGPL, allowing this function
 128  * to be invoked directly from non-LGPL code.
 129  */
 130 static inline int _urcu_mb_read_ongoing(void)
 131 {
 132         return URCU_TLS(urcu_mb_reader).ctr & URCU_GP_CTR_NEST_MASK;
 133 }
 134
 135 #ifdef __cplusplus
 136 }
 137 #endif
 138
 139 #endif /* _URCU_MB_STATIC_H */