1 /* rwsem.h: R/W semaphores, public interface
3 * Written by David Howells (dhowells@redhat.com).
4 * Derived from asm-i386/semaphore.h
10 #include <linux/linkage.h>
12 #include <linux/types.h>
13 #include <linux/kernel.h>
14 #include <linux/list.h>
15 #include <linux/spinlock.h>
17 #include <linux/atomic.h>
19 struct optimistic_spin_queue;
22 #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
23 #include <linux/rwsem-spinlock.h> /* use a generic implementation */
25 /* All arch specific implementations share the same struct */
28 raw_spinlock_t wait_lock;
29 struct list_head wait_list;
32 * Write owner. Used as a speculative check to see
33 * if the owner is running on the cpu.
35 struct task_struct *owner;
36 struct optimistic_spin_queue *osq; /* spinner MCS lock */
38 #ifdef CONFIG_DEBUG_LOCK_ALLOC
39 struct lockdep_map dep_map;
43 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
44 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
45 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
46 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
48 /* Include the arch specific part */
49 #include <asm/rwsem.h>
51 /* In all implementations count != 0 means locked */
52 static inline int rwsem_is_locked(struct rw_semaphore *sem)
54 return sem->count != 0;
59 /* Common initializer macros and functions */
61 #ifdef CONFIG_DEBUG_LOCK_ALLOC
62 # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
64 # define __RWSEM_DEP_MAP_INIT(lockname)
67 #if defined(CONFIG_SMP) && !defined(CONFIG_RWSEM_GENERIC_SPINLOCK)
68 #define __RWSEM_INITIALIZER(name) \
69 { RWSEM_UNLOCKED_VALUE, \
70 __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock), \
71 LIST_HEAD_INIT((name).wait_list), \
74 __RWSEM_DEP_MAP_INIT(name) }
76 #define __RWSEM_INITIALIZER(name) \
77 { RWSEM_UNLOCKED_VALUE, \
78 __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock), \
79 LIST_HEAD_INIT((name).wait_list) \
80 __RWSEM_DEP_MAP_INIT(name) }
83 #define DECLARE_RWSEM(name) \
84 struct rw_semaphore name = __RWSEM_INITIALIZER(name)
86 extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
87 struct lock_class_key *key);
89 #define init_rwsem(sem) \
91 static struct lock_class_key __key; \
93 __init_rwsem((sem), #sem, &__key); \
97 * This is the same regardless of which rwsem implementation that is being used.
98 * It is just a heuristic meant to be called by somebody alreadying holding the
99 * rwsem to see if somebody from an incompatible type is wanting access to the
102 static inline int rwsem_is_contended(struct rw_semaphore *sem)
104 return !list_empty(&sem->wait_list);
110 extern void down_read(struct rw_semaphore *sem);
113 * trylock for reading -- returns 1 if successful, 0 if contention
115 extern int down_read_trylock(struct rw_semaphore *sem);
120 extern void down_write(struct rw_semaphore *sem);
123 * trylock for writing -- returns 1 if successful, 0 if contention
125 extern int down_write_trylock(struct rw_semaphore *sem);
128 * release a read lock
130 extern void up_read(struct rw_semaphore *sem);
133 * release a write lock
135 extern void up_write(struct rw_semaphore *sem);
138 * downgrade write lock to read lock
140 extern void downgrade_write(struct rw_semaphore *sem);
142 #ifdef CONFIG_DEBUG_LOCK_ALLOC
144 * nested locking. NOTE: rwsems are not allowed to recurse
145 * (which occurs if the same task tries to acquire the same
146 * lock instance multiple times), but multiple locks of the
147 * same lock class might be taken, if the order of the locks
148 * is always the same. This ordering rule can be expressed
149 * to lockdep via the _nested() APIs, but enumerating the
150 * subclasses that are used. (If the nesting relationship is
151 * static then another method for expressing nested locking is
152 * the explicit definition of lock class keys and the use of
153 * lockdep_set_class() at lock initialization time.
154 * See Documentation/lockdep-design.txt for more details.)
156 extern void down_read_nested(struct rw_semaphore *sem, int subclass);
157 extern void down_write_nested(struct rw_semaphore *sem, int subclass);
158 extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock);
160 # define down_write_nest_lock(sem, nest_lock) \
162 typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
163 _down_write_nest_lock(sem, &(nest_lock)->dep_map); \
167 * Take/release a lock when not the owner will release it.
169 * [ This API should be avoided as much as possible - the
170 * proper abstraction for this case is completions. ]
172 extern void down_read_non_owner(struct rw_semaphore *sem);
173 extern void up_read_non_owner(struct rw_semaphore *sem);
175 # define down_read_nested(sem, subclass) down_read(sem)
176 # define down_write_nest_lock(sem, nest_lock) down_write(sem)
177 # define down_write_nested(sem, subclass) down_write(sem)
178 # define down_read_non_owner(sem) down_read(sem)
179 # define up_read_non_owner(sem) up_read(sem)
182 #endif /* _LINUX_RWSEM_H */