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 #include <stdlib.h>
  27 #include <assert.h>
  28 #include <limits.h>
  29 #include <unistd.h>
  30 #include <stdint.h>
  31 #include <stdbool.h>
  32 #include <glib.h>
  33
  34 #include "qemu/compiler.h"
  35 #include "qemu/thread.h"
  36 #include "qemu/queue.h"
  37 #include "qemu/atomic.h"
  38
  39 #ifdef __cplusplus
  40 extern "C" {
  41 #endif
  42
  43 /*
  44  * Important !
  45  *
  46  * Each thread containing read-side critical sections must be registered
  47  * with rcu_register_thread() before calling rcu_read_lock().
  48  * rcu_unregister_thread() should be called before the thread exits.
  49  */
  50
  51 #ifdef DEBUG_RCU
  52 #define rcu_assert(args...)    assert(args)
  53 #else
  54 #define rcu_assert(args...)
  55 #endif
  56
  57 /*
  58  * Global quiescent period counter with low-order bits unused.
  59  * Using a int rather than a char to eliminate false register dependencies
  60  * causing stalls on some architectures.
  61  */
  62 extern unsigned long rcu_gp_ctr;
  63
  64 extern QemuEvent rcu_gp_event;
  65
  66 struct rcu_reader_data {
  67     /* Data used by both reader and synchronize_rcu() */
  68     unsigned long ctr;
  69     bool waiting;
  70
  71     /* Data used by reader only */
  72     unsigned depth;
  73
  74     /* Data used for registry, protected by rcu_gp_lock */
  75     QLIST_ENTRY(rcu_reader_data) node;
  76 };
  77
  78 extern __thread struct rcu_reader_data rcu_reader;
  79
  80 static inline void rcu_read_lock(void)
  81 {
  82     struct rcu_reader_data *p_rcu_reader = &rcu_reader;
  83     unsigned ctr;
  84
  85     if (p_rcu_reader->depth++ > 0) {
  86         return;
  87     }
  88
  89     ctr = atomic_read(&rcu_gp_ctr);
  90     atomic_xchg(&p_rcu_reader->ctr, ctr);
  91     if (atomic_read(&p_rcu_reader->waiting)) {
  92         atomic_set(&p_rcu_reader->waiting, false);
  93         qemu_event_set(&rcu_gp_event);
  94     }
  95 }
  96
  97 static inline void rcu_read_unlock(void)
  98 {
  99     struct rcu_reader_data *p_rcu_reader = &rcu_reader;
 100
 101     assert(p_rcu_reader->depth != 0);
 102     if (--p_rcu_reader->depth > 0) {
 103         return;
 104     }
 105
 106     atomic_xchg(&p_rcu_reader->ctr, 0);
 107     if (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 struct rcu_head;
 122 typedef void RCUCBFunc(struct rcu_head *head);
 123
 124 struct rcu_head {
 125     struct rcu_head *next;
 126     RCUCBFunc *func;
 127 };
 128
 129 extern void call_rcu1(struct rcu_head *head, RCUCBFunc *func);
 130
 131 /* The operands of the minus operator must have the same type,
 132  * which must be the one that we specify in the cast.
 133  */
 134 #define call_rcu(head, func, field)                                      \
 135     call_rcu1(({                                                         \
 136          char __attribute__((unused))                                    \
 137             offset_must_be_zero[-offsetof(typeof(*(head)), field)],      \
 138             func_type_invalid = (func) - (void (*)(typeof(head)))(func); \
 139          &(head)->field;                                                 \
 140       }),                                                                \
 141       (RCUCBFunc *)(func))
 142
 143 #define g_free_rcu(obj, field) \
 144     call_rcu1(({                                                         \
 145         char __attribute__((unused))                                     \
 146             offset_must_be_zero[-offsetof(typeof(*(obj)), field)];       \
 147         &(obj)->field;                                                   \
 148       }),                                                                \
 149       (RCUCBFunc *)g_free);
 150
 151 #ifdef __cplusplus
 152 }
 153 #endif
 154
 155 #endif /* QEMU_RCU_H */