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