7 * Userspace RCU header with explicit memory barrier.
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.
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.
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
23 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
27 #include "qemu/thread.h"
28 #include "qemu/queue.h"
29 #include "qemu/atomic.h"
30 #include "qemu/sys_membarrier.h"
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.
45 #define rcu_assert(args...) assert(args)
47 #define rcu_assert(args...)
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.
55 extern unsigned long rcu_gp_ctr
;
57 extern QemuEvent rcu_gp_event
;
59 struct rcu_reader_data
{
60 /* Data used by both reader and synchronize_rcu() */
64 /* Data used by reader only */
67 /* Data used for registry, protected by rcu_registry_lock */
68 QLIST_ENTRY(rcu_reader_data
) node
;
71 extern __thread
struct rcu_reader_data rcu_reader
;
73 static inline void rcu_read_lock(void)
75 struct rcu_reader_data
*p_rcu_reader
= &rcu_reader
;
78 if (p_rcu_reader
->depth
++ > 0) {
82 ctr
= qatomic_read(&rcu_gp_ctr
);
83 qatomic_set(&p_rcu_reader
->ctr
, ctr
);
85 /* Write p_rcu_reader->ctr before reading RCU-protected pointers. */
89 static inline void rcu_read_unlock(void)
91 struct rcu_reader_data
*p_rcu_reader
= &rcu_reader
;
93 assert(p_rcu_reader
->depth
!= 0);
94 if (--p_rcu_reader
->depth
> 0) {
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.
103 qatomic_store_release(&p_rcu_reader
->ctr
, 0);
105 /* Write p_rcu_reader->ctr before reading p_rcu_reader->waiting. */
106 smp_mb_placeholder();
107 if (unlikely(qatomic_read(&p_rcu_reader
->waiting
))) {
108 qatomic_set(&p_rcu_reader
->waiting
, false);
109 qemu_event_set(&rcu_gp_event
);
113 extern void synchronize_rcu(void);
116 * Reader thread registration.
118 extern void rcu_register_thread(void);
119 extern void rcu_unregister_thread(void);
122 * Support for fork(). fork() support is enabled at startup.
124 extern void rcu_enable_atfork(void);
125 extern void rcu_disable_atfork(void);
128 typedef void RCUCBFunc(struct rcu_head
*head
);
131 struct rcu_head
*next
;
135 extern void call_rcu1(struct rcu_head
*head
, RCUCBFunc
*func
);
136 extern void drain_call_rcu(void);
138 /* The operands of the minus operator must have the same type,
139 * which must be the one that we specify in the cast.
141 #define call_rcu(head, func, field) \
143 char __attribute__((unused)) \
144 offset_must_be_zero[-offsetof(typeof(*(head)), field)], \
145 func_type_invalid = (func) - (void (*)(typeof(head)))(func); \
150 #define g_free_rcu(obj, field) \
152 char __attribute__((unused)) \
153 offset_must_be_zero[-offsetof(typeof(*(obj)), field)]; \
156 (RCUCBFunc *)g_free);
158 typedef void RCUReadAuto
;
159 static inline RCUReadAuto
*rcu_read_auto_lock(void)
162 /* Anything non-NULL causes the cleanup function to be called */
163 return (void *)(uintptr_t)0x1;
166 static inline void rcu_read_auto_unlock(RCUReadAuto
*r
)
171 G_DEFINE_AUTOPTR_CLEANUP_FUNC(RCUReadAuto
, rcu_read_auto_unlock
)
173 #define WITH_RCU_READ_LOCK_GUARD() \
174 WITH_RCU_READ_LOCK_GUARD_(glue(_rcu_read_auto, __COUNTER__))
176 #define WITH_RCU_READ_LOCK_GUARD_(var) \
177 for (g_autoptr(RCUReadAuto) var = rcu_read_auto_lock(); \
178 (var); rcu_read_auto_unlock(var), (var) = NULL)
180 #define RCU_READ_LOCK_GUARD() \
181 g_autoptr(RCUReadAuto) _rcu_read_auto __attribute__((unused)) = rcu_read_auto_lock()
187 #endif /* QEMU_RCU_H */