urcu-qsbr-static.h

   1 #ifndef _URCU_QSBR_STATIC_H
   2 #define _URCU_QSBR_STATIC_H
   3
   4 /*
   5  * urcu-qsbr-static.h
   6  *
   7  * Userspace RCU QSBR header.
   8  *
   9  * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu-qsbr.h for linking
  10  * dynamically with the userspace rcu QSBR library.
  11  *
  12  * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
  13  * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
  14  *
  15  * This library is free software; you can redistribute it and/or
  16  * modify it under the terms of the GNU Lesser General Public
  17  * License as published by the Free Software Foundation; either
  18  * version 2.1 of the License, or (at your option) any later version.
  19  *
  20  * This library is distributed in the hope that it will be useful,
  21  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  22  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  23  * Lesser General Public License for more details.
  24  *
  25  * You should have received a copy of the GNU Lesser General Public
  26  * License along with this library; if not, write to the Free Software
  27  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  28  *
  29  * IBM's contributions to this file may be relicensed under LGPLv2 or later.
  30  */
  31
  32 #include <stdlib.h>
  33 #include <pthread.h>
  34 #include <assert.h>
  35
  36 #include <compiler.h>
  37 #include <arch.h>
  38
  39 /*
  40  * Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
  41  */
  42 #define _LOAD_SHARED(p)        ACCESS_ONCE(p)
  43
  44 /*
  45  * Load a data from shared memory, doing a cache flush if required.
  46  */
  47 #define LOAD_SHARED(p)                  \
  48         ({                              \
  49                 smp_rmc();              \
  50                 _LOAD_SHARED(p);        \
  51         })
  52
  53 /*
  54  * Identify a shared store. A smp_wmc() or smp_mc() should follow the store.
  55  */
  56 #define _STORE_SHARED(x, v)     ({ ACCESS_ONCE(x) = (v); })
  57
  58 /*
  59  * Store v into x, where x is located in shared memory. Performs the required
  60  * cache flush after writing. Returns v.
  61  */
  62 #define STORE_SHARED(x, v)              \
  63         ({                              \
  64                 _STORE_SHARED(x, v);    \
  65                 smp_wmc();              \
  66                 (v);                    \
  67         })
  68
  69 /**
  70  * _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable
  71  * into a RCU read-side critical section. The pointer can later be safely
  72  * dereferenced within the critical section.
  73  *
  74  * This ensures that the pointer copy is invariant thorough the whole critical
  75  * section.
  76  *
  77  * Inserts memory barriers on architectures that require them (currently only
  78  * Alpha) and documents which pointers are protected by RCU.
  79  *
  80  * Should match rcu_assign_pointer() or rcu_xchg_pointer().
  81  */
  82
  83 #define _rcu_dereference(p)     ({                                      \
  84                                 typeof(p) _________p1 = LOAD_SHARED(p); \
  85                                 smp_read_barrier_depends();             \
  86                                 (_________p1);                          \
  87                                 })
  88
  89 /*
  90  * This code section can only be included in LGPL 2.1 compatible source code.
  91  * See below for the function call wrappers which can be used in code meant to
  92  * be only linked with the Userspace RCU library. This comes with a small
  93  * performance degradation on the read-side due to the added function calls.
  94  * This is required to permit relinking with newer versions of the library.
  95  */
  96
  97 /*
  98  * If a reader is really non-cooperative and refuses to commit its
  99  * rcu_reader_qs_gp count to memory (there is no barrier in the reader
 100  * per-se), kick it after a few loops waiting for it.
 101  */
 102 #define KICK_READER_LOOPS 10000
 103
 104 #ifdef DEBUG_RCU
 105 #define rcu_assert(args...)     assert(args)
 106 #else
 107 #define rcu_assert(args...)
 108 #endif
 109
 110 #ifdef DEBUG_YIELD
 111 #include <sched.h>
 112 #include <time.h>
 113 #include <pthread.h>
 114 #include <unistd.h>
 115
 116 #define YIELD_READ      (1 << 0)
 117 #define YIELD_WRITE     (1 << 1)
 118
 119 /* maximum sleep delay, in us */
 120 #define MAX_SLEEP 50
 121
 122 extern unsigned int yield_active;
 123 extern unsigned int __thread rand_yield;
 124
 125 static inline void debug_yield_read(void)
 126 {
 127         if (yield_active & YIELD_READ)
 128                 if (rand_r(&rand_yield) & 0x1)
 129                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
 130 }
 131
 132 static inline void debug_yield_write(void)
 133 {
 134         if (yield_active & YIELD_WRITE)
 135                 if (rand_r(&rand_yield) & 0x1)
 136                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
 137 }
 138
 139 static inline void debug_yield_init(void)
 140 {
 141         rand_yield = time(NULL) ^ pthread_self();
 142 }
 143 #else
 144 static inline void debug_yield_read(void)
 145 {
 146 }
 147
 148 static inline void debug_yield_write(void)
 149 {
 150 }
 151
 152 static inline void debug_yield_init(void)
 153 {
 154
 155 }
 156 #endif
 157
 158 static inline void reader_barrier()
 159 {
 160         smp_mb();
 161 }
 162
 163 /*
 164  * Global quiescent period counter with low-order bits unused.
 165  * Using a int rather than a char to eliminate false register dependencies
 166  * causing stalls on some architectures.
 167  */
 168 extern long urcu_gp_ctr;
 169
 170 extern long __thread rcu_reader_qs_gp;
 171
 172 static inline int rcu_gp_ongoing(long *value)
 173 {
 174         long reader_gp;
 175
 176         if (value == NULL)
 177                 return 0;
 178         reader_gp = LOAD_SHARED(*value);
 179         return reader_gp && (reader_gp - urcu_gp_ctr < 0);
 180 }
 181
 182 static inline void _rcu_read_lock(void)
 183 {
 184         rcu_assert(rcu_reader_qs_gp & 1);
 185 }
 186
 187 static inline void _rcu_read_unlock(void)
 188 {
 189 }
 190
 191 static inline void _rcu_quiescent_state(void)
 192 {
 193         smp_mb();
 194         _STORE_SHARED(rcu_reader_qs_gp, _LOAD_SHARED(urcu_gp_ctr));
 195         smp_mb();
 196 }
 197
 198 static inline void _rcu_thread_offline(void)
 199 {
 200         smp_mb();
 201         STORE_SHARED(rcu_reader_qs_gp, 0);
 202 }
 203
 204 static inline void _rcu_thread_online(void)
 205 {
 206         _STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr));
 207         smp_mb();
 208 }
 209
 210 /**
 211  * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
 212  * meant to be read by RCU read-side critical sections. Returns the assigned
 213  * value.
 214  *
 215  * Documents which pointers will be dereferenced by RCU read-side critical
 216  * sections and adds the required memory barriers on architectures requiring
 217  * them. It also makes sure the compiler does not reorder code initializing the
 218  * data structure before its publication.
 219  *
 220  * Should match rcu_dereference_pointer().
 221  */
 222
 223 #define _rcu_assign_pointer(p, v)                       \
 224         ({                                              \
 225                 if (!__builtin_constant_p(v) ||         \
 226                     ((v) != NULL))                      \
 227                         wmb();                          \
 228                 STORE_SHARED(p, v);                     \
 229         })
 230
 231 /**
 232  * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
 233  * pointer to the data structure, which can be safely freed after waiting for a
 234  * quiescent state using synchronize_rcu().
 235  */
 236
 237 #define _rcu_xchg_pointer(p, v)                         \
 238         ({                                              \
 239                 if (!__builtin_constant_p(v) ||         \
 240                     ((v) != NULL))                      \
 241                         wmb();                          \
 242                 xchg(p, v);                             \
 243         })
 244
 245 /*
 246  * Exchanges the pointer and waits for quiescent state.
 247  * The pointer returned can be freed.
 248  */
 249 #define _rcu_publish_content(p, v)                      \
 250         ({                                              \
 251                 void *oldptr;                           \
 252                 oldptr = _rcu_xchg_pointer(p, v);       \
 253                 synchronize_rcu();                      \
 254                 oldptr;                                 \
 255         })
 256
 257 #endif /* _URCU_QSBR_STATIC_H */