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 #include <syscall.h>
  37 #include <unistd.h>
  38
  39 #include <urcu/compiler.h>
  40 #include <urcu/arch.h>
  41 #include <urcu/arch_uatomic.h>
  42 #include <urcu/list.h>
  43
  44 /*
  45  * Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
  46  */
  47 #define _LOAD_SHARED(p)        ACCESS_ONCE(p)
  48
  49 /*
  50  * Load a data from shared memory, doing a cache flush if required.
  51  */
  52 #define LOAD_SHARED(p)                  \
  53         ({                              \
  54                 smp_rmc();              \
  55                 _LOAD_SHARED(p);        \
  56         })
  57
  58 /*
  59  * Identify a shared store. A smp_wmc() or smp_mc() should follow the store.
  60  */
  61 #define _STORE_SHARED(x, v)     ({ ACCESS_ONCE(x) = (v); })
  62
  63 /*
  64  * Store v into x, where x is located in shared memory. Performs the required
  65  * cache flush after writing. Returns v.
  66  */
  67 #define STORE_SHARED(x, v)              \
  68         ({                              \
  69                 _STORE_SHARED(x, v);    \
  70                 smp_wmc();              \
  71                 (v);                    \
  72         })
  73
  74 /**
  75  * _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable
  76  * into a RCU read-side critical section. The pointer can later be safely
  77  * dereferenced within the critical section.
  78  *
  79  * This ensures that the pointer copy is invariant thorough the whole critical
  80  * section.
  81  *
  82  * Inserts memory barriers on architectures that require them (currently only
  83  * Alpha) and documents which pointers are protected by RCU.
  84  *
  85  * Should match rcu_assign_pointer() or rcu_xchg_pointer().
  86  */
  87
  88 #define _rcu_dereference(p)     ({                                      \
  89                                 typeof(p) _________p1 = LOAD_SHARED(p); \
  90                                 smp_read_barrier_depends();             \
  91                                 (_________p1);                          \
  92                                 })
  93
  94 #define futex(...)              syscall(__NR_futex, __VA_ARGS__)
  95 #define FUTEX_WAIT              0
  96 #define FUTEX_WAKE              1
  97
  98 /*
  99  * This code section can only be included in LGPL 2.1 compatible source code.
 100  * See below for the function call wrappers which can be used in code meant to
 101  * be only linked with the Userspace RCU library. This comes with a small
 102  * performance degradation on the read-side due to the added function calls.
 103  * This is required to permit relinking with newer versions of the library.
 104  */
 105
 106 /*
 107  * If a reader is really non-cooperative and refuses to commit its
 108  * urcu_reader.ctr count to memory (there is no barrier in the reader
 109  * per-se), kick it after a few loops waiting for it.
 110  */
 111 #define KICK_READER_LOOPS 10000
 112
 113 /*
 114  * Active attempts to check for reader Q.S. before calling futex().
 115  */
 116 #define RCU_QS_ACTIVE_ATTEMPTS 100
 117
 118 #ifdef DEBUG_RCU
 119 #define rcu_assert(args...)     assert(args)
 120 #else
 121 #define rcu_assert(args...)
 122 #endif
 123
 124 #ifdef DEBUG_YIELD
 125 #include <sched.h>
 126 #include <time.h>
 127 #include <pthread.h>
 128 #include <unistd.h>
 129
 130 #define YIELD_READ      (1 << 0)
 131 #define YIELD_WRITE     (1 << 1)
 132
 133 /* maximum sleep delay, in us */
 134 #define MAX_SLEEP 50
 135
 136 extern unsigned int yield_active;
 137 extern unsigned int __thread rand_yield;
 138
 139 static inline void debug_yield_read(void)
 140 {
 141         if (yield_active & YIELD_READ)
 142                 if (rand_r(&rand_yield) & 0x1)
 143                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
 144 }
 145
 146 static inline void debug_yield_write(void)
 147 {
 148         if (yield_active & YIELD_WRITE)
 149                 if (rand_r(&rand_yield) & 0x1)
 150                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
 151 }
 152
 153 static inline void debug_yield_init(void)
 154 {
 155         rand_yield = time(NULL) ^ pthread_self();
 156 }
 157 #else
 158 static inline void debug_yield_read(void)
 159 {
 160 }
 161
 162 static inline void debug_yield_write(void)
 163 {
 164 }
 165
 166 static inline void debug_yield_init(void)
 167 {
 168
 169 }
 170 #endif
 171
 172 static inline void reader_barrier()
 173 {
 174         smp_mb();
 175 }
 176
 177 #define RCU_GP_ONLINE           (1UL << 0)
 178 #define RCU_GP_CTR              (1UL << 1)
 179
 180 /*
 181  * Global quiescent period counter with low-order bits unused.
 182  * Using a int rather than a char to eliminate false register dependencies
 183  * causing stalls on some architectures.
 184  */
 185 extern unsigned long urcu_gp_ctr;
 186
 187 struct urcu_reader {
 188         /* Data used by both reader and synchronize_rcu() */
 189         unsigned long ctr;
 190         /* Data used for registry */
 191         struct list_head head __attribute__((aligned(CACHE_LINE_SIZE)));
 192         pthread_t tid;
 193 };
 194
 195 extern struct urcu_reader __thread urcu_reader;
 196
 197 extern int gp_futex;
 198
 199 /*
 200  * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
 201  */
 202 static inline void wake_up_gp(void)
 203 {
 204         if (unlikely(uatomic_read(&gp_futex) == -1)) {
 205                 uatomic_set(&gp_futex, 0);
 206                 futex(&gp_futex, FUTEX_WAKE, 1,
 207                       NULL, NULL, 0);
 208         }
 209 }
 210
 211 #if (BITS_PER_LONG < 64)
 212 static inline int rcu_gp_ongoing(unsigned long *value)
 213 {
 214         unsigned long reader_gp;
 215
 216         if (value == NULL)
 217                 return 0;
 218         reader_gp = LOAD_SHARED(*value);
 219         return reader_gp && ((reader_gp ^ urcu_gp_ctr) & RCU_GP_CTR);
 220 }
 221 #else /* !(BITS_PER_LONG < 64) */
 222 static inline int rcu_gp_ongoing(unsigned long *value)
 223 {
 224         unsigned long reader_gp;
 225
 226         if (value == NULL)
 227                 return 0;
 228         reader_gp = LOAD_SHARED(*value);
 229         return reader_gp && (reader_gp - urcu_gp_ctr > ULONG_MAX / 2);
 230 }
 231 #endif  /* !(BITS_PER_LONG < 64) */
 232
 233 static inline void _rcu_read_lock(void)
 234 {
 235         rcu_assert(urcu_reader.ctr);
 236 }
 237
 238 static inline void _rcu_read_unlock(void)
 239 {
 240 }
 241
 242 static inline void _rcu_quiescent_state(void)
 243 {
 244         smp_mb();
 245         _STORE_SHARED(urcu_reader.ctr, _LOAD_SHARED(urcu_gp_ctr));
 246         smp_mb();       /* write urcu_reader.ctr before read futex */
 247         wake_up_gp();
 248         smp_mb();
 249 }
 250
 251 static inline void _rcu_thread_offline(void)
 252 {
 253         smp_mb();
 254         STORE_SHARED(urcu_reader.ctr, 0);
 255         smp_mb();       /* write urcu_reader.ctr before read futex */
 256         wake_up_gp();
 257 }
 258
 259 static inline void _rcu_thread_online(void)
 260 {
 261         _STORE_SHARED(urcu_reader.ctr, LOAD_SHARED(urcu_gp_ctr));
 262         smp_mb();
 263 }
 264
 265 /**
 266  * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
 267  * meant to be read by RCU read-side critical sections. Returns the assigned
 268  * value.
 269  *
 270  * Documents which pointers will be dereferenced by RCU read-side critical
 271  * sections and adds the required memory barriers on architectures requiring
 272  * them. It also makes sure the compiler does not reorder code initializing the
 273  * data structure before its publication.
 274  *
 275  * Should match rcu_dereference_pointer().
 276  */
 277
 278 #define _rcu_assign_pointer(p, v)                       \
 279         ({                                              \
 280                 if (!__builtin_constant_p(v) ||         \
 281                     ((v) != NULL))                      \
 282                         wmb();                          \
 283                 STORE_SHARED(p, v);                     \
 284         })
 285
 286 /**
 287  * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer
 288  * is as expected by "old". If succeeds, returns the previous pointer to the
 289  * data structure, which can be safely freed after waiting for a quiescent state
 290  * using synchronize_rcu(). If fails (unexpected value), returns old (which
 291  * should not be freed !).
 292  */
 293
 294 #define _rcu_cmpxchg_pointer(p, old, _new)              \
 295         ({                                              \
 296                 if (!__builtin_constant_p(_new) ||      \
 297                     ((_new) != NULL))                   \
 298                         wmb();                          \
 299                 uatomic_cmpxchg(p, old, _new);          \
 300         })
 301
 302 /**
 303  * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
 304  * pointer to the data structure, which can be safely freed after waiting for a
 305  * quiescent state using synchronize_rcu().
 306  */
 307
 308 #define _rcu_xchg_pointer(p, v)                         \
 309         ({                                              \
 310                 if (!__builtin_constant_p(v) ||         \
 311                     ((v) != NULL))                      \
 312                         wmb();                          \
 313                 uatomic_xchg(p, v);                     \
 314         })
 315
 316 /*
 317  * Exchanges the pointer and waits for quiescent state.
 318  * The pointer returned can be freed.
 319  */
 320 #define _rcu_publish_content(p, v)                      \
 321         ({                                              \
 322                 void *oldptr;                           \
 323                 oldptr = _rcu_xchg_pointer(p, v);       \
 324                 synchronize_rcu();                      \
 325                 oldptr;                                 \
 326         })
 327
 328 #endif /* _URCU_QSBR_STATIC_H */