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 #include <limits.h>
  36
  37 #include <compiler.h>
  38 #include <arch.h>
  39
  40 /*
  41  * Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
  42  */
  43 #define _LOAD_SHARED(p)        ACCESS_ONCE(p)
  44
  45 /*
  46  * Load a data from shared memory, doing a cache flush if required.
  47  */
  48 #define LOAD_SHARED(p)                  \
  49         ({                              \
  50                 smp_rmc();              \
  51                 _LOAD_SHARED(p);        \
  52         })
  53
  54 /*
  55  * Identify a shared store. A smp_wmc() or smp_mc() should follow the store.
  56  */
  57 #define _STORE_SHARED(x, v)     ({ ACCESS_ONCE(x) = (v); })
  58
  59 /*
  60  * Store v into x, where x is located in shared memory. Performs the required
  61  * cache flush after writing. Returns v.
  62  */
  63 #define STORE_SHARED(x, v)              \
  64         ({                              \
  65                 _STORE_SHARED(x, v);    \
  66                 smp_wmc();              \
  67                 (v);                    \
  68         })
  69
  70 /**
  71  * _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable
  72  * into a RCU read-side critical section. The pointer can later be safely
  73  * dereferenced within the critical section.
  74  *
  75  * This ensures that the pointer copy is invariant thorough the whole critical
  76  * section.
  77  *
  78  * Inserts memory barriers on architectures that require them (currently only
  79  * Alpha) and documents which pointers are protected by RCU.
  80  *
  81  * Should match rcu_assign_pointer() or rcu_xchg_pointer().
  82  */
  83
  84 #define _rcu_dereference(p)     ({                                      \
  85                                 typeof(p) _________p1 = LOAD_SHARED(p); \
  86                                 smp_read_barrier_depends();             \
  87                                 (_________p1);                          \
  88                                 })
  89
  90 /*
  91  * This code section can only be included in LGPL 2.1 compatible source code.
  92  * See below for the function call wrappers which can be used in code meant to
  93  * be only linked with the Userspace RCU library. This comes with a small
  94  * performance degradation on the read-side due to the added function calls.
  95  * This is required to permit relinking with newer versions of the library.
  96  */
  97
  98 /*
  99  * If a reader is really non-cooperative and refuses to commit its
 100  * rcu_reader_qs_gp count to memory (there is no barrier in the reader
 101  * per-se), kick it after a few loops waiting for it.
 102  */
 103 #define KICK_READER_LOOPS 10000
 104
 105 #ifdef DEBUG_RCU
 106 #define rcu_assert(args...)     assert(args)
 107 #else
 108 #define rcu_assert(args...)
 109 #endif
 110
 111 #ifdef DEBUG_YIELD
 112 #include <sched.h>
 113 #include <time.h>
 114 #include <pthread.h>
 115 #include <unistd.h>
 116
 117 #define YIELD_READ      (1 << 0)
 118 #define YIELD_WRITE     (1 << 1)
 119
 120 /* maximum sleep delay, in us */
 121 #define MAX_SLEEP 50
 122
 123 extern unsigned int yield_active;
 124 extern unsigned int __thread rand_yield;
 125
 126 static inline void debug_yield_read(void)
 127 {
 128         if (yield_active & YIELD_READ)
 129                 if (rand_r(&rand_yield) & 0x1)
 130                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
 131 }
 132
 133 static inline void debug_yield_write(void)
 134 {
 135         if (yield_active & YIELD_WRITE)
 136                 if (rand_r(&rand_yield) & 0x1)
 137                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
 138 }
 139
 140 static inline void debug_yield_init(void)
 141 {
 142         rand_yield = time(NULL) ^ pthread_self();
 143 }
 144 #else
 145 static inline void debug_yield_read(void)
 146 {
 147 }
 148
 149 static inline void debug_yield_write(void)
 150 {
 151 }
 152
 153 static inline void debug_yield_init(void)
 154 {
 155
 156 }
 157 #endif
 158
 159 static inline void reader_barrier()
 160 {
 161         smp_mb();
 162 }
 163
 164 #define RCU_GP_ONLINE           (1UL << 0)
 165 #define RCU_GP_CTR              (1UL << 1)
 166
 167 /*
 168  * Global quiescent period counter with low-order bits unused.
 169  * Using a int rather than a char to eliminate false register dependencies
 170  * causing stalls on some architectures.
 171  */
 172 extern unsigned long urcu_gp_ctr;
 173
 174 extern unsigned long __thread rcu_reader_qs_gp;
 175
 176 static inline int rcu_gp_ongoing(unsigned long *value)
 177 {
 178         unsigned long reader_gp;
 179
 180         if (value == NULL)
 181                 return 0;
 182         reader_gp = LOAD_SHARED(*value);
 183         return reader_gp && (reader_gp - urcu_gp_ctr > ULONG_MAX / 2);
 184 }
 185
 186 static inline void _rcu_read_lock(void)
 187 {
 188         rcu_assert(rcu_reader_qs_gp);
 189 }
 190
 191 static inline void _rcu_read_unlock(void)
 192 {
 193 }
 194
 195 static inline void _rcu_quiescent_state(void)
 196 {
 197         smp_mb();
 198         _STORE_SHARED(rcu_reader_qs_gp, _LOAD_SHARED(urcu_gp_ctr));
 199         smp_mb();
 200 }
 201
 202 static inline void _rcu_thread_offline(void)
 203 {
 204         smp_mb();
 205         STORE_SHARED(rcu_reader_qs_gp, 0);
 206 }
 207
 208 static inline void _rcu_thread_online(void)
 209 {
 210         _STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr));
 211         smp_mb();
 212 }
 213
 214 /**
 215  * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
 216  * meant to be read by RCU read-side critical sections. Returns the assigned
 217  * value.
 218  *
 219  * Documents which pointers will be dereferenced by RCU read-side critical
 220  * sections and adds the required memory barriers on architectures requiring
 221  * them. It also makes sure the compiler does not reorder code initializing the
 222  * data structure before its publication.
 223  *
 224  * Should match rcu_dereference_pointer().
 225  */
 226
 227 #define _rcu_assign_pointer(p, v)                       \
 228         ({                                              \
 229                 if (!__builtin_constant_p(v) ||         \
 230                     ((v) != NULL))                      \
 231                         wmb();                          \
 232                 STORE_SHARED(p, v);                     \
 233         })
 234
 235 /**
 236  * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
 237  * pointer to the data structure, which can be safely freed after waiting for a
 238  * quiescent state using synchronize_rcu().
 239  */
 240
 241 #define _rcu_xchg_pointer(p, v)                         \
 242         ({                                              \
 243                 if (!__builtin_constant_p(v) ||         \
 244                     ((v) != NULL))                      \
 245                         wmb();                          \
 246                 xchg(p, v);                             \
 247         })
 248
 249 /*
 250  * Exchanges the pointer and waits for quiescent state.
 251  * The pointer returned can be freed.
 252  */
 253 #define _rcu_publish_content(p, v)                      \
 254         ({                                              \
 255                 void *oldptr;                           \
 256                 oldptr = _rcu_xchg_pointer(p, v);       \
 257                 synchronize_rcu();                      \
 258                 oldptr;                                 \
 259         })
 260
 261 #endif /* _URCU_QSBR_STATIC_H */