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