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>
16 #include <linux/atomic.h>
17 #include <linux/err.h>
18 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
19 #include <linux/osq_lock.h>
24 #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
25 #include <linux/rwsem-spinlock.h> /* use a generic implementation */
27 /* All arch specific implementations share the same struct */
30 struct list_head wait_list;
31 raw_spinlock_t wait_lock;
32 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
33 struct optimistic_spin_queue osq; /* spinner MCS lock */
35 * Write owner. Used as a speculative check to see
36 * if the owner is running on the cpu.
38 struct task_struct *owner;
40 #ifdef CONFIG_DEBUG_LOCK_ALLOC
41 struct lockdep_map dep_map;
45 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
46 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
47 extern struct rw_semaphore *rwsem_down_write_failed_killable(struct rw_semaphore *sem);
48 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
49 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
51 /* Include the arch specific part */
52 #include <asm/rwsem.h>
54 /* In all implementations count != 0 means locked */
55 static inline int rwsem_is_locked(struct rw_semaphore *sem)
57 return sem->count != 0;
62 /* Common initializer macros and functions */
64 #ifdef CONFIG_DEBUG_LOCK_ALLOC
65 # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
67 # define __RWSEM_DEP_MAP_INIT(lockname)
70 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
71 #define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL
73 #define __RWSEM_OPT_INIT(lockname)
76 #define __RWSEM_INITIALIZER(name) \
77 { .count = RWSEM_UNLOCKED_VALUE, \
78 .wait_list = LIST_HEAD_INIT((name).wait_list), \
79 .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \
80 __RWSEM_OPT_INIT(name) \
81 __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);
121 extern int __must_check down_write_killable(struct rw_semaphore *sem);
124 * trylock for writing -- returns 1 if successful, 0 if contention
126 extern int down_write_trylock(struct rw_semaphore *sem);
129 * release a read lock
131 extern void up_read(struct rw_semaphore *sem);
134 * release a write lock
136 extern void up_write(struct rw_semaphore *sem);
139 * downgrade write lock to read lock
141 extern void downgrade_write(struct rw_semaphore *sem);
143 #ifdef CONFIG_DEBUG_LOCK_ALLOC
145 * nested locking. NOTE: rwsems are not allowed to recurse
146 * (which occurs if the same task tries to acquire the same
147 * lock instance multiple times), but multiple locks of the
148 * same lock class might be taken, if the order of the locks
149 * is always the same. This ordering rule can be expressed
150 * to lockdep via the _nested() APIs, but enumerating the
151 * subclasses that are used. (If the nesting relationship is
152 * static then another method for expressing nested locking is
153 * the explicit definition of lock class keys and the use of
154 * lockdep_set_class() at lock initialization time.
155 * See Documentation/locking/lockdep-design.txt for more details.)
157 extern void down_read_nested(struct rw_semaphore *sem, int subclass);
158 extern void down_write_nested(struct rw_semaphore *sem, int subclass);
159 extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass);
160 extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock);
162 # define down_write_nest_lock(sem, nest_lock) \
164 typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
165 _down_write_nest_lock(sem, &(nest_lock)->dep_map); \
169 * Take/release a lock when not the owner will release it.
171 * [ This API should be avoided as much as possible - the
172 * proper abstraction for this case is completions. ]
174 extern void down_read_non_owner(struct rw_semaphore *sem);
175 extern void up_read_non_owner(struct rw_semaphore *sem);
177 # define down_read_nested(sem, subclass) down_read(sem)
178 # define down_write_nest_lock(sem, nest_lock) down_write(sem)
179 # define down_write_nested(sem, subclass) down_write(sem)
180 # define down_write_killable_nested(sem, subclass) down_write_killable(sem)
181 # define down_read_non_owner(sem) down_read(sem)
182 # define up_read_non_owner(sem) up_read(sem)
185 #endif /* _LINUX_RWSEM_H */