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 #include "qemu/coroutine-tls.h"
  33
  34 #ifdef __cplusplus
  35 extern "C" {
  36 #endif
  37
  38 /*
  39  * Important !
  40  *
  41  * Each thread containing read-side critical sections must be registered
  42  * with rcu_register_thread() before calling rcu_read_lock().
  43  * rcu_unregister_thread() should be called before the thread exits.
  44  */
  45
  46 #ifdef DEBUG_RCU
  47 #define rcu_assert(args...)    assert(args)
  48 #else
  49 #define rcu_assert(args...)
  50 #endif
  51
  52 /*
  53  * Global quiescent period counter with low-order bits unused.
  54  * Using a int rather than a char to eliminate false register dependencies
  55  * causing stalls on some architectures.
  56  */
  57 extern unsigned long rcu_gp_ctr;
  58
  59 extern QemuEvent rcu_gp_event;
  60
  61 struct rcu_reader_data {
  62     /* Data used by both reader and synchronize_rcu() */
  63     unsigned long ctr;
  64     bool waiting;
  65
  66     /* Data used by reader only */
  67     unsigned depth;
  68
  69     /* Data used for registry, protected by rcu_registry_lock */
  70     QLIST_ENTRY(rcu_reader_data) node;
  71
  72     /*
  73      * NotifierList used to force an RCU grace period.  Accessed under
  74      * rcu_registry_lock.  Note that the notifier is called _outside_
  75      * the thread!
  76      */
  77     NotifierList force_rcu;
  78 };
  79
  80 QEMU_DECLARE_CO_TLS(struct rcu_reader_data, rcu_reader)
  81
  82 static inline void rcu_read_lock(void)
  83 {
  84     struct rcu_reader_data *p_rcu_reader = get_ptr_rcu_reader();
  85     unsigned ctr;
  86
  87     if (p_rcu_reader->depth++ > 0) {
  88         return;
  89     }
  90
  91     ctr = qatomic_read(&rcu_gp_ctr);
  92     qatomic_set(&p_rcu_reader->ctr, ctr);
  93
  94     /* Write p_rcu_reader->ctr before reading RCU-protected pointers.  */
  95     smp_mb_placeholder();
  96 }
  97
  98 static inline void rcu_read_unlock(void)
  99 {
 100     struct rcu_reader_data *p_rcu_reader = get_ptr_rcu_reader();
 101
 102     assert(p_rcu_reader->depth != 0);
 103     if (--p_rcu_reader->depth > 0) {
 104         return;
 105     }
 106
 107     /* Ensure that the critical section is seen to precede the
 108      * store to p_rcu_reader->ctr.  Together with the following
 109      * smp_mb_placeholder(), this ensures writes to p_rcu_reader->ctr
 110      * are sequentially consistent.
 111      */
 112     qatomic_store_release(&p_rcu_reader->ctr, 0);
 113
 114     /* Write p_rcu_reader->ctr before reading p_rcu_reader->waiting.  */
 115     smp_mb_placeholder();
 116     if (unlikely(qatomic_read(&p_rcu_reader->waiting))) {
 117         qatomic_set(&p_rcu_reader->waiting, false);
 118         qemu_event_set(&rcu_gp_event);
 119     }
 120 }
 121
 122 extern void synchronize_rcu(void);
 123
 124 /*
 125  * Reader thread registration.
 126  */
 127 extern void rcu_register_thread(void);
 128 extern void rcu_unregister_thread(void);
 129
 130 /*
 131  * Support for fork().  fork() support is enabled at startup.
 132  */
 133 extern void rcu_enable_atfork(void);
 134 extern void rcu_disable_atfork(void);
 135
 136 struct rcu_head;
 137 typedef void RCUCBFunc(struct rcu_head *head);
 138
 139 struct rcu_head {
 140     struct rcu_head *next;
 141     RCUCBFunc *func;
 142 };
 143
 144 extern void call_rcu1(struct rcu_head *head, RCUCBFunc *func);
 145 extern void drain_call_rcu(void);
 146
 147 /* The operands of the minus operator must have the same type,
 148  * which must be the one that we specify in the cast.
 149  */
 150 #define call_rcu(head, func, field)                                      \
 151     call_rcu1(({                                                         \
 152          char __attribute__((unused))                                    \
 153             offset_must_be_zero[-offsetof(typeof(*(head)), field)],      \
 154             func_type_invalid = (func) - (void (*)(typeof(head)))(func); \
 155          &(head)->field;                                                 \
 156       }),                                                                \
 157       (RCUCBFunc *)(func))
 158
 159 #define g_free_rcu(obj, field) \
 160     call_rcu1(({                                                         \
 161         char __attribute__((unused))                                     \
 162             offset_must_be_zero[-offsetof(typeof(*(obj)), field)];       \
 163         &(obj)->field;                                                   \
 164       }),                                                                \
 165       (RCUCBFunc *)g_free);
 166
 167 typedef void RCUReadAuto;
 168 static inline RCUReadAuto *rcu_read_auto_lock(void)
 169 {
 170     rcu_read_lock();
 171     /* Anything non-NULL causes the cleanup function to be called */
 172     return (void *)(uintptr_t)0x1;
 173 }
 174
 175 static inline void rcu_read_auto_unlock(RCUReadAuto *r)
 176 {
 177     rcu_read_unlock();
 178 }
 179
 180 G_DEFINE_AUTOPTR_CLEANUP_FUNC(RCUReadAuto, rcu_read_auto_unlock)
 181
 182 #define WITH_RCU_READ_LOCK_GUARD() \
 183     WITH_RCU_READ_LOCK_GUARD_(glue(_rcu_read_auto, __COUNTER__))
 184
 185 #define WITH_RCU_READ_LOCK_GUARD_(var) \
 186     for (g_autoptr(RCUReadAuto) var = rcu_read_auto_lock(); \
 187         (var); rcu_read_auto_unlock(var), (var) = NULL)
 188
 189 #define RCU_READ_LOCK_GUARD() \
 190     g_autoptr(RCUReadAuto) _rcu_read_auto __attribute__((unused)) = rcu_read_auto_lock()
 191
 192 /*
 193  * Force-RCU notifiers tell readers that they should exit their
 194  * read-side critical section.
 195  */
 196 void rcu_add_force_rcu_notifier(Notifier *n);
 197 void rcu_remove_force_rcu_notifier(Notifier *n);
 198
 199 #ifdef __cplusplus
 200 }
 201 #endif
 202
 203 #endif /* QEMU_RCU_H */