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 #include "qemu/sys_membarrier.h"
  31
  32 #ifdef __cplusplus
  33 extern "C" {
  34 #endif
  35
  36 /*
  37  * Important !
  38  *
  39  * Each thread containing read-side critical sections must be registered
  40  * with rcu_register_thread() before calling rcu_read_lock().
  41  * rcu_unregister_thread() should be called before the thread exits.
  42  */
  43
  44 #ifdef DEBUG_RCU
  45 #define rcu_assert(args...)    assert(args)
  46 #else
  47 #define rcu_assert(args...)
  48 #endif
  49
  50 /*
  51  * Global quiescent period counter with low-order bits unused.
  52  * Using a int rather than a char to eliminate false register dependencies
  53  * causing stalls on some architectures.
  54  */
  55 extern unsigned long rcu_gp_ctr;
  56
  57 extern QemuEvent rcu_gp_event;
  58
  59 struct rcu_reader_data {
  60     /* Data used by both reader and synchronize_rcu() */
  61     unsigned long ctr;
  62     bool waiting;
  63
  64     /* Data used by reader only */
  65     unsigned depth;
  66
  67     /* Data used for registry, protected by rcu_registry_lock */
  68     QLIST_ENTRY(rcu_reader_data) node;
  69 };
  70
  71 extern __thread struct rcu_reader_data rcu_reader;
  72
  73 static inline void rcu_read_lock(void)
  74 {
  75     struct rcu_reader_data *p_rcu_reader = &rcu_reader;
  76     unsigned ctr;
  77
  78     if (p_rcu_reader->depth++ > 0) {
  79         return;
  80     }
  81
  82     ctr = atomic_read(&rcu_gp_ctr);
  83     atomic_set(&p_rcu_reader->ctr, ctr);
  84
  85     /* Write p_rcu_reader->ctr before reading RCU-protected pointers.  */
  86     smp_mb_placeholder();
  87 }
  88
  89 static inline void rcu_read_unlock(void)
  90 {
  91     struct rcu_reader_data *p_rcu_reader = &rcu_reader;
  92
  93     assert(p_rcu_reader->depth != 0);
  94     if (--p_rcu_reader->depth > 0) {
  95         return;
  96     }
  97
  98     /* Ensure that the critical section is seen to precede the
  99      * store to p_rcu_reader->ctr.  Together with the following
 100      * smp_mb_placeholder(), this ensures writes to p_rcu_reader->ctr
 101      * are sequentially consistent.
 102      */
 103     atomic_store_release(&p_rcu_reader->ctr, 0);
 104
 105     /* Write p_rcu_reader->ctr before reading p_rcu_reader->waiting.  */
 106     smp_mb_placeholder();
 107     if (unlikely(atomic_read(&p_rcu_reader->waiting))) {
 108         atomic_set(&p_rcu_reader->waiting, false);
 109         qemu_event_set(&rcu_gp_event);
 110     }
 111 }
 112
 113 extern void synchronize_rcu(void);
 114
 115 /*
 116  * Reader thread registration.
 117  */
 118 extern void rcu_register_thread(void);
 119 extern void rcu_unregister_thread(void);
 120
 121 /*
 122  * Support for fork().  fork() support is enabled at startup.
 123  */
 124 extern void rcu_enable_atfork(void);
 125 extern void rcu_disable_atfork(void);
 126
 127 struct rcu_head;
 128 typedef void RCUCBFunc(struct rcu_head *head);
 129
 130 struct rcu_head {
 131     struct rcu_head *next;
 132     RCUCBFunc *func;
 133 };
 134
 135 extern void call_rcu1(struct rcu_head *head, RCUCBFunc *func);
 136
 137 /* The operands of the minus operator must have the same type,
 138  * which must be the one that we specify in the cast.
 139  */
 140 #define call_rcu(head, func, field)                                      \
 141     call_rcu1(({                                                         \
 142          char __attribute__((unused))                                    \
 143             offset_must_be_zero[-offsetof(typeof(*(head)), field)],      \
 144             func_type_invalid = (func) - (void (*)(typeof(head)))(func); \
 145          &(head)->field;                                                 \
 146       }),                                                                \
 147       (RCUCBFunc *)(func))
 148
 149 #define g_free_rcu(obj, field) \
 150     call_rcu1(({                                                         \
 151         char __attribute__((unused))                                     \
 152             offset_must_be_zero[-offsetof(typeof(*(obj)), field)];       \
 153         &(obj)->field;                                                   \
 154       }),                                                                \
 155       (RCUCBFunc *)g_free);
 156
 157 #ifdef __cplusplus
 158 }
 159 #endif
 160
 161 #endif /* QEMU_RCU_H */