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TOMOYO Linux Cross Reference
Linux/include/linux/rwsem.h

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  1 /* rwsem.h: R/W semaphores, public interface
  2  *
  3  * Written by David Howells (dhowells@redhat.com).
  4  * Derived from asm-i386/semaphore.h
  5  */
  6 
  7 #ifndef _LINUX_RWSEM_H
  8 #define _LINUX_RWSEM_H
  9 
 10 #include <linux/linkage.h>
 11 
 12 #include <linux/types.h>
 13 #include <linux/kernel.h>
 14 #include <linux/list.h>
 15 #include <linux/spinlock.h>
 16 #include <linux/atomic.h>
 17 #include <linux/err.h>
 18 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
 19 #include <linux/osq_lock.h>
 20 #endif
 21 
 22 struct rw_semaphore;
 23 
 24 #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
 25 #include <linux/rwsem-spinlock.h> /* use a generic implementation */
 26 #define __RWSEM_INIT_COUNT(name)        .count = RWSEM_UNLOCKED_VALUE
 27 #else
 28 /* All arch specific implementations share the same struct */
 29 struct rw_semaphore {
 30         atomic_long_t count;
 31         struct list_head wait_list;
 32         raw_spinlock_t wait_lock;
 33 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
 34         struct optimistic_spin_queue osq; /* spinner MCS lock */
 35         /*
 36          * Write owner. Used as a speculative check to see
 37          * if the owner is running on the cpu.
 38          */
 39         struct task_struct *owner;
 40 #endif
 41 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 42         struct lockdep_map      dep_map;
 43 #endif
 44 };
 45 
 46 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
 47 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
 48 extern struct rw_semaphore *rwsem_down_write_failed_killable(struct rw_semaphore *sem);
 49 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
 50 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
 51 
 52 /* Include the arch specific part */
 53 #include <asm/rwsem.h>
 54 
 55 /* In all implementations count != 0 means locked */
 56 static inline int rwsem_is_locked(struct rw_semaphore *sem)
 57 {
 58         return atomic_long_read(&sem->count) != 0;
 59 }
 60 
 61 #define __RWSEM_INIT_COUNT(name)        .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE)
 62 #endif
 63 
 64 /* Common initializer macros and functions */
 65 
 66 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 67 # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
 68 #else
 69 # define __RWSEM_DEP_MAP_INIT(lockname)
 70 #endif
 71 
 72 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
 73 #define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL
 74 #else
 75 #define __RWSEM_OPT_INIT(lockname)
 76 #endif
 77 
 78 #define __RWSEM_INITIALIZER(name)                               \
 79         { __RWSEM_INIT_COUNT(name),                             \
 80           .wait_list = LIST_HEAD_INIT((name).wait_list),        \
 81           .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \
 82           __RWSEM_OPT_INIT(name)                                \
 83           __RWSEM_DEP_MAP_INIT(name) }
 84 
 85 #define DECLARE_RWSEM(name) \
 86         struct rw_semaphore name = __RWSEM_INITIALIZER(name)
 87 
 88 extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
 89                          struct lock_class_key *key);
 90 
 91 #define init_rwsem(sem)                                         \
 92 do {                                                            \
 93         static struct lock_class_key __key;                     \
 94                                                                 \
 95         __init_rwsem((sem), #sem, &__key);                      \
 96 } while (0)
 97 
 98 /*
 99  * This is the same regardless of which rwsem implementation that is being used.
100  * It is just a heuristic meant to be called by somebody alreadying holding the
101  * rwsem to see if somebody from an incompatible type is wanting access to the
102  * lock.
103  */
104 static inline int rwsem_is_contended(struct rw_semaphore *sem)
105 {
106         return !list_empty(&sem->wait_list);
107 }
108 
109 /*
110  * lock for reading
111  */
112 extern void down_read(struct rw_semaphore *sem);
113 
114 /*
115  * trylock for reading -- returns 1 if successful, 0 if contention
116  */
117 extern int down_read_trylock(struct rw_semaphore *sem);
118 
119 /*
120  * lock for writing
121  */
122 extern void down_write(struct rw_semaphore *sem);
123 extern int __must_check down_write_killable(struct rw_semaphore *sem);
124 
125 /*
126  * trylock for writing -- returns 1 if successful, 0 if contention
127  */
128 extern int down_write_trylock(struct rw_semaphore *sem);
129 
130 /*
131  * release a read lock
132  */
133 extern void up_read(struct rw_semaphore *sem);
134 
135 /*
136  * release a write lock
137  */
138 extern void up_write(struct rw_semaphore *sem);
139 
140 /*
141  * downgrade write lock to read lock
142  */
143 extern void downgrade_write(struct rw_semaphore *sem);
144 
145 #ifdef CONFIG_DEBUG_LOCK_ALLOC
146 /*
147  * nested locking. NOTE: rwsems are not allowed to recurse
148  * (which occurs if the same task tries to acquire the same
149  * lock instance multiple times), but multiple locks of the
150  * same lock class might be taken, if the order of the locks
151  * is always the same. This ordering rule can be expressed
152  * to lockdep via the _nested() APIs, but enumerating the
153  * subclasses that are used. (If the nesting relationship is
154  * static then another method for expressing nested locking is
155  * the explicit definition of lock class keys and the use of
156  * lockdep_set_class() at lock initialization time.
157  * See Documentation/locking/lockdep-design.txt for more details.)
158  */
159 extern void down_read_nested(struct rw_semaphore *sem, int subclass);
160 extern void down_write_nested(struct rw_semaphore *sem, int subclass);
161 extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass);
162 extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock);
163 
164 # define down_write_nest_lock(sem, nest_lock)                   \
165 do {                                                            \
166         typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
167         _down_write_nest_lock(sem, &(nest_lock)->dep_map);      \
168 } while (0);
169 
170 /*
171  * Take/release a lock when not the owner will release it.
172  *
173  * [ This API should be avoided as much as possible - the
174  *   proper abstraction for this case is completions. ]
175  */
176 extern void down_read_non_owner(struct rw_semaphore *sem);
177 extern void up_read_non_owner(struct rw_semaphore *sem);
178 #else
179 # define down_read_nested(sem, subclass)                down_read(sem)
180 # define down_write_nest_lock(sem, nest_lock)   down_write(sem)
181 # define down_write_nested(sem, subclass)       down_write(sem)
182 # define down_write_killable_nested(sem, subclass)      down_write_killable(sem)
183 # define down_read_non_owner(sem)               down_read(sem)
184 # define up_read_non_owner(sem)                 up_read(sem)
185 #endif
186 
187 #endif /* _LINUX_RWSEM_H */
188 

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