include/qemu/rcu.h

   1 #ifndef QEMU_RCU_H
   2 #define QEMU_RCU_H
   3
   4 /*
   5  * urcu-mb.h
   6  *
   7  * Userspace RCU header with explicit memory barrier.
   8  *
   9  * This library is free software; you can redistribute it and/or
  10  * modify it under the terms of the GNU Lesser General Public
  11  * License as published by the Free Software Foundation; either
  12  * version 2.1 of the License, or (at your option) any later version.
  13  *
  14  * This library is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  17  * Lesser General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU Lesser General Public
  20  * License along with this library; if not, write to the Free Software
  21  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  22  *
  23  * IBM's contributions to this file may be relicensed under LGPLv2 or later.
  24  */
  25
  26
  27 #include "qemu/thread.h"
  28 #include "qemu/queue.h"
  29 #include "qemu/atomic.h"
  30
  31 #ifdef __cplusplus
  32 extern "C" {
  33 #endif
  34
  35 /*
  36  * Important !
  37  *
  38  * Each thread containing read-side critical sections must be registered
  39  * with rcu_register_thread() before calling rcu_read_lock().
  40  * rcu_unregister_thread() should be called before the thread exits.
  41  */
  42
  43 #ifdef DEBUG_RCU
  44 #define rcu_assert(args...)    assert(args)
  45 #else
  46 #define rcu_assert(args...)
  47 #endif
  48
  49 /*
  50  * Global quiescent period counter with low-order bits unused.
  51  * Using a int rather than a char to eliminate false register dependencies
  52  * causing stalls on some architectures.
  53  */
  54 extern unsigned long rcu_gp_ctr;
  55
  56 extern QemuEvent rcu_gp_event;
  57
  58 struct rcu_reader_data {
  59     /* Data used by both reader and synchronize_rcu() */
  60     unsigned long ctr;
  61     bool waiting;
  62
  63     /* Data used by reader only */
  64     unsigned depth;
  65
  66     /* Data used for registry, protected by rcu_registry_lock */
  67     QLIST_ENTRY(rcu_reader_data) node;
  68 };
  69
  70 extern __thread struct rcu_reader_data rcu_reader;
  71
  72 static inline void rcu_read_lock(void)
  73 {
  74     struct rcu_reader_data *p_rcu_reader = &rcu_reader;
  75     unsigned ctr;
  76
  77     if (p_rcu_reader->depth++ > 0) {
  78         return;
  79     }
  80
  81     ctr = atomic_read(&rcu_gp_ctr);
  82     atomic_set(&p_rcu_reader->ctr, ctr);
  83
  84     /* Write p_rcu_reader->ctr before reading RCU-protected pointers.  */
  85     smp_mb();
  86 }
  87
  88 static inline void rcu_read_unlock(void)
  89 {
  90     struct rcu_reader_data *p_rcu_reader = &rcu_reader;
  91
  92     assert(p_rcu_reader->depth != 0);
  93     if (--p_rcu_reader->depth > 0) {
  94         return;
  95     }
  96
  97     /* Ensure that the critical section is seen to precede the
  98      * store to p_rcu_reader->ctr.  Together with the following
  99      * smp_mb(), this ensures writes to p_rcu_reader->ctr
 100      * are sequentially consistent.
 101      */
 102     atomic_store_release(&p_rcu_reader->ctr, 0);
 103
 104     /* Write p_rcu_reader->ctr before reading p_rcu_reader->waiting.  */
 105     smp_mb();
 106     if (unlikely(atomic_read(&p_rcu_reader->waiting))) {
 107         atomic_set(&p_rcu_reader->waiting, false);
 108         qemu_event_set(&rcu_gp_event);
 109     }
 110 }
 111
 112 extern void synchronize_rcu(void);
 113
 114 /*
 115  * Reader thread registration.
 116  */
 117 extern void rcu_register_thread(void);
 118 extern void rcu_unregister_thread(void);
 119
 120 /*
 121  * Support for fork().  fork() support is enabled at startup.
 122  */
 123 extern void rcu_enable_atfork(void);
 124 extern void rcu_disable_atfork(void);
 125
 126 struct rcu_head;
 127 typedef void RCUCBFunc(struct rcu_head *head);
 128
 129 struct rcu_head {
 130     struct rcu_head *next;
 131     RCUCBFunc *func;
 132 };
 133
 134 extern void call_rcu1(struct rcu_head *head, RCUCBFunc *func);
 135
 136 /* The operands of the minus operator must have the same type,
 137  * which must be the one that we specify in the cast.
 138  */
 139 #define call_rcu(head, func, field)                                      \
 140     call_rcu1(({                                                         \
 141          char __attribute__((unused))                                    \
 142             offset_must_be_zero[-offsetof(typeof(*(head)), field)],      \
 143             func_type_invalid = (func) - (void (*)(typeof(head)))(func); \
 144          &(head)->field;                                                 \
 145       }),                                                                \
 146       (RCUCBFunc *)(func))
 147
 148 #define g_free_rcu(obj, field) \
 149     call_rcu1(({                                                         \
 150         char __attribute__((unused))                                     \
 151             offset_must_be_zero[-offsetof(typeof(*(obj)), field)];       \
 152         &(obj)->field;                                                   \
 153       }),                                                                \
 154       (RCUCBFunc *)g_free);
 155
 156 #ifdef __cplusplus
 157 }
 158 #endif
 159
 160 #endif /* QEMU_RCU_H */