urcu-static.h

   1 #ifndef _URCU_STATIC_H
   2 #define _URCU_STATIC_H
   3
   4 /*
   5  * urcu-static.h
   6  *
   7  * Userspace RCU header.
   8  *
   9  * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See urcu.h for linking
  10  * dynamically with the userspace rcu 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
  35 #include <compiler.h>
  36 #include <arch.h>
  37
  38 /*
  39  * Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
  40  */
  41 #define _LOAD_SHARED(p)        ACCESS_ONCE(p)
  42
  43 /*
  44  * Load a data from shared memory, doing a cache flush if required.
  45  */
  46 #define LOAD_SHARED(p)                  \
  47         ({                              \
  48                 smp_rmc();              \
  49                 _LOAD_SHARED(p);        \
  50         })
  51
  52 /*
  53  * Identify a shared store. A smp_wmc() or smp_mc() should follow the store.
  54  */
  55 #define _STORE_SHARED(x, v)     ({ ACCESS_ONCE(x) = (v); })
  56
  57 /*
  58  * Store v into x, where x is located in shared memory. Performs the required
  59  * cache flush after writing. Returns v.
  60  */
  61 #define STORE_SHARED(x, v)              \
  62         ({                              \
  63                 _STORE_SHARED(x, v);    \
  64                 smp_wmc();              \
  65                 (v);                    \
  66         })
  67
  68 /**
  69  * _rcu_dereference - reads (copy) a RCU-protected pointer to a local variable
  70  * into a RCU read-side critical section. The pointer can later be safely
  71  * dereferenced within the critical section.
  72  *
  73  * This ensures that the pointer copy is invariant thorough the whole critical
  74  * section.
  75  *
  76  * Inserts memory barriers on architectures that require them (currently only
  77  * Alpha) and documents which pointers are protected by RCU.
  78  *
  79  * Should match rcu_assign_pointer() or rcu_xchg_pointer().
  80  */
  81
  82 #define _rcu_dereference(p)     ({                                      \
  83                                 typeof(p) _________p1 = LOAD_SHARED(p); \
  84                                 smp_read_barrier_depends();             \
  85                                 (_________p1);                          \
  86                                 })
  87
  88 /*
  89  * This code section can only be included in LGPL 2.1 compatible source code.
  90  * See below for the function call wrappers which can be used in code meant to
  91  * be only linked with the Userspace RCU library. This comes with a small
  92  * performance degradation on the read-side due to the added function calls.
  93  * This is required to permit relinking with newer versions of the library.
  94  */
  95
  96 /*
  97  * The signal number used by the RCU library can be overridden with
  98  * -DSIGURCU= when compiling the library.
  99  */
 100 #ifndef SIGURCU
 101 #define SIGURCU SIGUSR1
 102 #endif
 103
 104 /*
 105  * If a reader is really non-cooperative and refuses to commit its
 106  * urcu_active_readers 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 #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 /* Updates without DEBUG_FULL_MB are much slower. Account this in the delay */
 121 #ifdef DEBUG_FULL_MB
 122 /* maximum sleep delay, in us */
 123 #define MAX_SLEEP 50
 124 #else
 125 #define MAX_SLEEP 30000
 126 #endif
 127
 128 extern unsigned int yield_active;
 129 extern unsigned int __thread rand_yield;
 130
 131 static inline void debug_yield_read(void)
 132 {
 133         if (yield_active & YIELD_READ)
 134                 if (rand_r(&rand_yield) & 0x1)
 135                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
 136 }
 137
 138 static inline void debug_yield_write(void)
 139 {
 140         if (yield_active & YIELD_WRITE)
 141                 if (rand_r(&rand_yield) & 0x1)
 142                         usleep(rand_r(&rand_yield) % MAX_SLEEP);
 143 }
 144
 145 static inline void debug_yield_init(void)
 146 {
 147         rand_yield = time(NULL) ^ pthread_self();
 148 }
 149 #else
 150 static inline void debug_yield_read(void)
 151 {
 152 }
 153
 154 static inline void debug_yield_write(void)
 155 {
 156 }
 157
 158 static inline void debug_yield_init(void)
 159 {
 160
 161 }
 162 #endif
 163
 164 #ifdef DEBUG_FULL_MB
 165 static inline void reader_barrier()
 166 {
 167         smp_mb();
 168 }
 169 #else
 170 static inline void reader_barrier()
 171 {
 172         barrier();
 173 }
 174 #endif
 175
 176 /*
 177  * The trick here is that RCU_GP_CTR_BIT must be a multiple of 8 so we can use a
 178  * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
 179  */
 180 #define RCU_GP_COUNT            (1UL << 0)
 181 /* Use the amount of bits equal to half of the architecture long size */
 182 #define RCU_GP_CTR_BIT          (1UL << (sizeof(long) << 2))
 183 #define RCU_GP_CTR_NEST_MASK    (RCU_GP_CTR_BIT - 1)
 184
 185 /*
 186  * Global quiescent period counter with low-order bits unused.
 187  * Using a int rather than a char to eliminate false register dependencies
 188  * causing stalls on some architectures.
 189  */
 190 extern long urcu_gp_ctr;
 191
 192 extern long __thread urcu_active_readers;
 193
 194 static inline int rcu_old_gp_ongoing(long *value)
 195 {
 196         long v;
 197
 198         if (value == NULL)
 199                 return 0;
 200         /*
 201          * Make sure both tests below are done on the same version of *value
 202          * to insure consistency.
 203          */
 204         v = LOAD_SHARED(*value);
 205         return (v & RCU_GP_CTR_NEST_MASK) &&
 206                  ((v ^ urcu_gp_ctr) & RCU_GP_CTR_BIT);
 207 }
 208
 209 static inline void _rcu_read_lock(void)
 210 {
 211         long tmp;
 212
 213         tmp = urcu_active_readers;
 214         /* urcu_gp_ctr = RCU_GP_COUNT | (~RCU_GP_CTR_BIT or RCU_GP_CTR_BIT) */
 215         /*
 216          * The data dependency "read urcu_gp_ctr, write urcu_active_readers",
 217          * serializes those two memory operations. The memory barrier in the
 218          * signal handler ensures we receive the proper memory commit barriers
 219          * required by _STORE_SHARED and _LOAD_SHARED whenever communication
 220          * with the writer is needed.
 221          */
 222         if (likely(!(tmp & RCU_GP_CTR_NEST_MASK)))
 223                 _STORE_SHARED(urcu_active_readers, _LOAD_SHARED(urcu_gp_ctr));
 224         else
 225                 _STORE_SHARED(urcu_active_readers, tmp + RCU_GP_COUNT);
 226         /*
 227          * Increment active readers count before accessing the pointer.
 228          * See force_mb_all_threads().
 229          */
 230         reader_barrier();
 231 }
 232
 233 static inline void _rcu_read_unlock(void)
 234 {
 235         reader_barrier();
 236         /*
 237          * Finish using rcu before decrementing the pointer.
 238          * See force_mb_all_threads().
 239          */
 240         _STORE_SHARED(urcu_active_readers, urcu_active_readers - RCU_GP_COUNT);
 241 }
 242
 243 /**
 244  * _rcu_assign_pointer - assign (publicize) a pointer to a new data structure
 245  * meant to be read by RCU read-side critical sections. Returns the assigned
 246  * value.
 247  *
 248  * Documents which pointers will be dereferenced by RCU read-side critical
 249  * sections and adds the required memory barriers on architectures requiring
 250  * them. It also makes sure the compiler does not reorder code initializing the
 251  * data structure before its publication.
 252  *
 253  * Should match rcu_dereference_pointer().
 254  */
 255
 256 #define _rcu_assign_pointer(p, v)                       \
 257         ({                                              \
 258                 if (!__builtin_constant_p(v) ||         \
 259                     ((v) != NULL))                      \
 260                         wmb();                          \
 261                 STORE_SHARED(p, v);                     \
 262         })
 263
 264 /**
 265  * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
 266  * pointer to the data structure, which can be safely freed after waitin for a
 267  * quiescent state using synchronize_rcu().
 268  */
 269
 270 #define _rcu_xchg_pointer(p, v)                         \
 271         ({                                              \
 272                 if (!__builtin_constant_p(v) ||         \
 273                     ((v) != NULL))                      \
 274                         wmb();                          \
 275                 xchg(p, v);                             \
 276         })
 277
 278 /*
 279  * Exchanges the pointer and waits for quiescent state.
 280  * The pointer returned can be freed.
 281  */
 282 #define _rcu_publish_content(p, v)                      \
 283         ({                                              \
 284                 void *oldptr;                           \
 285                 oldptr = _rcu_xchg_pointer(p, v);       \
 286                 synchronize_rcu();                      \
 287                 oldptr;                                 \
 288         })
 289
 290 #endif /* _URCU_STATIC_H */