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/notify.h"
  31 #include "qemu/sys_membarrier.h"
  32
  33 #ifdef __cplusplus
  34 extern "C" {
  35 #endif
  36
  37 /*
  38  * Important !
  39  *
  40  * Each thread containing read-side critical sections must be registered
  41  * with rcu_register_thread() before calling rcu_read_lock().
  42  * rcu_unregister_thread() should be called before the thread exits.
  43  */
  44
  45 #ifdef DEBUG_RCU
  46 #define rcu_assert(args...)    assert(args)
  47 #else
  48 #define rcu_assert(args...)
  49 #endif
  50
  51 /*
  52  * Global quiescent period counter with low-order bits unused.
  53  * Using a int rather than a char to eliminate false register dependencies
  54  * causing stalls on some architectures.
  55  */
  56 extern unsigned long rcu_gp_ctr;
  57
  58 extern QemuEvent rcu_gp_event;
  59
  60 struct rcu_reader_data {
  61     /* Data used by both reader and synchronize_rcu() */
  62     unsigned long ctr;
  63     bool waiting;
  64
  65     /* Data used by reader only */
  66     unsigned depth;
  67
  68     /* Data used for registry, protected by rcu_registry_lock */
  69     QLIST_ENTRY(rcu_reader_data) node;
  70
  71     /*
  72      * NotifierList used to force an RCU grace period.  Accessed under
  73      * rcu_registry_lock.  Note that the notifier is called _outside_
  74      * the thread!
  75      */
  76     NotifierList force_rcu;
  77 };
  78
  79 extern __thread struct rcu_reader_data rcu_reader;
  80
  81 static inline void rcu_read_lock(void)
  82 {
  83     struct rcu_reader_data *p_rcu_reader = &rcu_reader;
  84     unsigned ctr;
  85
  86     if (p_rcu_reader->depth++ > 0) {
  87         return;
  88     }
  89
  90     ctr = qatomic_read(&rcu_gp_ctr);
  91     qatomic_set(&p_rcu_reader->ctr, ctr);
  92
  93     /* Write p_rcu_reader->ctr before reading RCU-protected pointers.  */
  94     smp_mb_placeholder();
  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     /* Ensure that the critical section is seen to precede the
 107      * store to p_rcu_reader->ctr.  Together with the following
 108      * smp_mb_placeholder(), this ensures writes to p_rcu_reader->ctr
 109      * are sequentially consistent.
 110      */
 111     qatomic_store_release(&p_rcu_reader->ctr, 0);
 112
 113     /* Write p_rcu_reader->ctr before reading p_rcu_reader->waiting.  */
 114     smp_mb_placeholder();
 115     if (unlikely(qatomic_read(&p_rcu_reader->waiting))) {
 116         qatomic_set(&p_rcu_reader->waiting, false);
 117         qemu_event_set(&rcu_gp_event);
 118     }
 119 }
 120
 121 extern void synchronize_rcu(void);
 122
 123 /*
 124  * Reader thread registration.
 125  */
 126 extern void rcu_register_thread(void);
 127 extern void rcu_unregister_thread(void);
 128
 129 /*
 130  * Support for fork().  fork() support is enabled at startup.
 131  */
 132 extern void rcu_enable_atfork(void);
 133 extern void rcu_disable_atfork(void);
 134
 135 struct rcu_head;
 136 typedef void RCUCBFunc(struct rcu_head *head);
 137
 138 struct rcu_head {
 139     struct rcu_head *next;
 140     RCUCBFunc *func;
 141 };
 142
 143 extern void call_rcu1(struct rcu_head *head, RCUCBFunc *func);
 144 extern void drain_call_rcu(void);
 145
 146 /* The operands of the minus operator must have the same type,
 147  * which must be the one that we specify in the cast.
 148  */
 149 #define call_rcu(head, func, field)                                      \
 150     call_rcu1(({                                                         \
 151          char __attribute__((unused))                                    \
 152             offset_must_be_zero[-offsetof(typeof(*(head)), field)],      \
 153             func_type_invalid = (func) - (void (*)(typeof(head)))(func); \
 154          &(head)->field;                                                 \
 155       }),                                                                \
 156       (RCUCBFunc *)(func))
 157
 158 #define g_free_rcu(obj, field) \
 159     call_rcu1(({                                                         \
 160         char __attribute__((unused))                                     \
 161             offset_must_be_zero[-offsetof(typeof(*(obj)), field)];       \
 162         &(obj)->field;                                                   \
 163       }),                                                                \
 164       (RCUCBFunc *)g_free);
 165
 166 typedef void RCUReadAuto;
 167 static inline RCUReadAuto *rcu_read_auto_lock(void)
 168 {
 169     rcu_read_lock();
 170     /* Anything non-NULL causes the cleanup function to be called */
 171     return (void *)(uintptr_t)0x1;
 172 }
 173
 174 static inline void rcu_read_auto_unlock(RCUReadAuto *r)
 175 {
 176     rcu_read_unlock();
 177 }
 178
 179 G_DEFINE_AUTOPTR_CLEANUP_FUNC(RCUReadAuto, rcu_read_auto_unlock)
 180
 181 #define WITH_RCU_READ_LOCK_GUARD() \
 182     WITH_RCU_READ_LOCK_GUARD_(glue(_rcu_read_auto, __COUNTER__))
 183
 184 #define WITH_RCU_READ_LOCK_GUARD_(var) \
 185     for (g_autoptr(RCUReadAuto) var = rcu_read_auto_lock(); \
 186         (var); rcu_read_auto_unlock(var), (var) = NULL)
 187
 188 #define RCU_READ_LOCK_GUARD() \
 189     g_autoptr(RCUReadAuto) _rcu_read_auto __attribute__((unused)) = rcu_read_auto_lock()
 190
 191 /*
 192  * Force-RCU notifiers tell readers that they should exit their
 193  * read-side critical section.
 194  */
 195 void rcu_add_force_rcu_notifier(Notifier *n);
 196 void rcu_remove_force_rcu_notifier(Notifier *n);
 197
 198 #ifdef __cplusplus
 199 }
 200 #endif
 201
 202 #endif /* QEMU_RCU_H */