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Rev | Author | Line No. | Line |
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5272 | serge | 1 | /* rwsem.h: R/W semaphores, public interface |
2 | * |
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3 | * Written by David Howells (dhowells@redhat.com). |
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4 | * Derived from asm-i386/semaphore.h |
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5 | */ |
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6 | |||
7 | #ifndef _LINUX_RWSEM_H |
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8 | #define _LINUX_RWSEM_H |
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9 | |||
10 | #include |
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11 | |||
12 | #include |
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13 | #include |
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14 | #include |
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15 | #include |
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16 | #include |
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17 | #ifdef CONFIG_RWSEM_SPIN_ON_OWNER |
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18 | #include |
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19 | #endif |
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20 | |||
21 | struct rw_semaphore; |
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22 | |||
23 | #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK |
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24 | #include |
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25 | #else |
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26 | /* All arch specific implementations share the same struct */ |
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27 | struct rw_semaphore { |
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5345 | serge | 28 | struct list_head wait_list; |
5272 | serge | 29 | long count; |
30 | raw_spinlock_t wait_lock; |
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31 | #ifdef CONFIG_RWSEM_SPIN_ON_OWNER |
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32 | struct optimistic_spin_queue osq; /* spinner MCS lock */ |
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33 | /* |
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34 | * Write owner. Used as a speculative check to see |
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35 | * if the owner is running on the cpu. |
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36 | */ |
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37 | struct task_struct *owner; |
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38 | #endif |
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39 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
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40 | struct lockdep_map dep_map; |
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41 | #endif |
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42 | }; |
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43 | |||
44 | extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem); |
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45 | extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem); |
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46 | extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *); |
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47 | extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem); |
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48 | |||
49 | /* Include the arch specific part */ |
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50 | #include |
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51 | |||
52 | /* In all implementations count != 0 means locked */ |
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53 | static inline int rwsem_is_locked(struct rw_semaphore *sem) |
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54 | { |
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55 | return sem->count != 0; |
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56 | } |
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57 | |||
58 | #endif |
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59 | |||
60 | /* Common initializer macros and functions */ |
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61 | |||
62 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
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63 | # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname } |
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64 | #else |
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65 | # define __RWSEM_DEP_MAP_INIT(lockname) |
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66 | #endif |
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67 | |||
68 | #ifdef CONFIG_RWSEM_SPIN_ON_OWNER |
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69 | #define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL |
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70 | #else |
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71 | #define __RWSEM_OPT_INIT(lockname) |
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72 | #endif |
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73 | |||
74 | #define __RWSEM_INITIALIZER(name) \ |
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75 | { .count = RWSEM_UNLOCKED_VALUE, \ |
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76 | .wait_list = LIST_HEAD_INIT((name).wait_list), \ |
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77 | .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \ |
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78 | __RWSEM_OPT_INIT(name) \ |
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79 | __RWSEM_DEP_MAP_INIT(name) } |
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80 | |||
81 | #define DECLARE_RWSEM(name) \ |
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82 | struct rw_semaphore name = __RWSEM_INITIALIZER(name) |
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83 | |||
84 | extern void __init_rwsem(struct rw_semaphore *sem, const char *name, |
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85 | struct lock_class_key *key); |
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86 | |||
87 | #define init_rwsem(sem) \ |
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88 | do { \ |
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89 | static struct lock_class_key __key; \ |
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90 | \ |
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91 | __init_rwsem((sem), #sem, &__key); \ |
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92 | } while (0) |
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93 | |||
94 | /* |
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95 | * This is the same regardless of which rwsem implementation that is being used. |
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96 | * It is just a heuristic meant to be called by somebody alreadying holding the |
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97 | * rwsem to see if somebody from an incompatible type is wanting access to the |
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98 | * lock. |
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99 | */ |
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100 | static inline int rwsem_is_contended(struct rw_semaphore *sem) |
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101 | { |
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102 | return !list_empty(&sem->wait_list); |
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103 | } |
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104 | |||
105 | /* |
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106 | * lock for reading |
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107 | */ |
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108 | extern void down_read(struct rw_semaphore *sem); |
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109 | |||
110 | /* |
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111 | * trylock for reading -- returns 1 if successful, 0 if contention |
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112 | */ |
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113 | extern int down_read_trylock(struct rw_semaphore *sem); |
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114 | |||
115 | /* |
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116 | * lock for writing |
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117 | */ |
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118 | extern void down_write(struct rw_semaphore *sem); |
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119 | |||
120 | /* |
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121 | * trylock for writing -- returns 1 if successful, 0 if contention |
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122 | */ |
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123 | extern int down_write_trylock(struct rw_semaphore *sem); |
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124 | |||
125 | /* |
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126 | * release a read lock |
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127 | */ |
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128 | extern void up_read(struct rw_semaphore *sem); |
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129 | |||
130 | /* |
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131 | * release a write lock |
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132 | */ |
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133 | extern void up_write(struct rw_semaphore *sem); |
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134 | |||
135 | /* |
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136 | * downgrade write lock to read lock |
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137 | */ |
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138 | extern void downgrade_write(struct rw_semaphore *sem); |
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139 | |||
140 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
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141 | /* |
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142 | * nested locking. NOTE: rwsems are not allowed to recurse |
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143 | * (which occurs if the same task tries to acquire the same |
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144 | * lock instance multiple times), but multiple locks of the |
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145 | * same lock class might be taken, if the order of the locks |
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146 | * is always the same. This ordering rule can be expressed |
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147 | * to lockdep via the _nested() APIs, but enumerating the |
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148 | * subclasses that are used. (If the nesting relationship is |
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149 | * static then another method for expressing nested locking is |
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150 | * the explicit definition of lock class keys and the use of |
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151 | * lockdep_set_class() at lock initialization time. |
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152 | * See Documentation/locking/lockdep-design.txt for more details.) |
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153 | */ |
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154 | extern void down_read_nested(struct rw_semaphore *sem, int subclass); |
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155 | extern void down_write_nested(struct rw_semaphore *sem, int subclass); |
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156 | extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock); |
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157 | |||
158 | # define down_write_nest_lock(sem, nest_lock) \ |
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159 | do { \ |
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160 | typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \ |
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161 | _down_write_nest_lock(sem, &(nest_lock)->dep_map); \ |
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162 | } while (0); |
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163 | |||
164 | /* |
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165 | * Take/release a lock when not the owner will release it. |
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166 | * |
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167 | * [ This API should be avoided as much as possible - the |
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168 | * proper abstraction for this case is completions. ] |
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169 | */ |
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170 | extern void down_read_non_owner(struct rw_semaphore *sem); |
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171 | extern void up_read_non_owner(struct rw_semaphore *sem); |
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172 | #else |
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173 | # define down_read_nested(sem, subclass) down_read(sem) |
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174 | # define down_write_nest_lock(sem, nest_lock) down_write(sem) |
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175 | # define down_write_nested(sem, subclass) down_write(sem) |
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176 | # define down_read_non_owner(sem) down_read(sem) |
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177 | # define up_read_non_owner(sem) up_read(sem) |
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178 | #endif |
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179 | |||
180 | #endif /* _LINUX_RWSEM_H */ |