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