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
33extern "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 */
55extern unsigned long rcu_gp_ctr;
56
57extern QemuEvent rcu_gp_event;
58
59struct 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
71extern __thread struct rcu_reader_data rcu_reader;
72
73static 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
89static 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
113extern void synchronize_rcu(void);
114
115/*
116 * Reader thread registration.
117 */
118extern void rcu_register_thread(void);
119extern void rcu_unregister_thread(void);
120
121/*
122 * Support for fork(). fork() support is enabled at startup.
123 */
124extern void rcu_enable_atfork(void);
125extern void rcu_disable_atfork(void);
126
127struct rcu_head;
128typedef void RCUCBFunc(struct rcu_head *head);
129
130struct rcu_head {
131 struct rcu_head *next;
132 RCUCBFunc *func;
133};
134
135extern 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 */
162