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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, see
21 * <https://www.gnu.org/licenses/>.
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 /*
35 * Important !
36 *
37 * Each thread containing read-side critical sections must be registered
38 * with rcu_register_thread() before calling rcu_read_lock().
39 * rcu_unregister_thread() should be called before the thread exits.
40 */
41
42 #ifdef DEBUG_RCU
43 #define rcu_assert(args...) assert(args)
44 #else
45 #define rcu_assert(args...)
46 #endif
47
48 /*
49 * Global quiescent period counter with low-order bits unused.
50 * Using a int rather than a char to eliminate false register dependencies
51 * causing stalls on some architectures.
52 */
53 extern unsigned long rcu_gp_ctr;
54
55 extern QemuEvent rcu_gp_event;
56
57 struct rcu_reader_data {
58 /* Data used by both reader and synchronize_rcu() */
59 unsigned long ctr;
60 bool waiting;
61
62 /* Data used by reader only */
63 unsigned depth;
64
65 /* Data used for registry, protected by rcu_registry_lock */
66 QLIST_ENTRY(rcu_reader_data) node;
67
68 /*
69 * NotifierList used to force an RCU grace period. Accessed under
70 * rcu_registry_lock. Note that the notifier is called _outside_
71 * the thread!
72 */
73 NotifierList force_rcu;
74 };
75
76 QEMU_DECLARE_CO_TLS(struct rcu_reader_data, rcu_reader)
77
78 static inline void rcu_read_lock(void)
79 {
80 struct rcu_reader_data *p_rcu_reader = get_ptr_rcu_reader();
81 unsigned ctr;
82
83 if (p_rcu_reader->depth++ > 0) {
84 return;
85 }
86
87 ctr = qatomic_read(&rcu_gp_ctr);
88 qatomic_set(&p_rcu_reader->ctr, ctr);
89
90 /*
91 * Read rcu_gp_ptr and write p_rcu_reader->ctr before reading
92 * RCU-protected pointers.
93 */
94 smp_mb_placeholder();
95 }
96
97 static inline void rcu_read_unlock(void)
98 {
99 struct rcu_reader_data *p_rcu_reader = get_ptr_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 void synchronize_rcu(void);
122
123 /*
124 * Reader thread registration.
125 */
126 void rcu_register_thread(void);
127 void rcu_unregister_thread(void);
128
129 /*
130 * Support for fork(). fork() support is enabled at startup.
131 */
132 void rcu_enable_atfork(void);
133 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 void call_rcu1(struct rcu_head *head, RCUCBFunc *func);
144 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 #endif /* QEMU_RCU_H */