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