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 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
18 #include <linux/osq_lock.h>
21 #ifdef CONFIG_PREEMPT_RT_FULL
22 #include <linux/rwsem_rt.h>
23 #else /* PREEMPT_RT_FULL */
27 #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
28 #include <linux/rwsem-spinlock.h> /* use a generic implementation */
30 /* All arch specific implementations share the same struct */
33 struct list_head wait_list;
34 raw_spinlock_t wait_lock;
35 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
36 struct optimistic_spin_queue osq; /* spinner MCS lock */
38 * Write owner. Used as a speculative check to see
39 * if the owner is running on the cpu.
41 struct task_struct *owner;
43 #ifdef CONFIG_DEBUG_LOCK_ALLOC
44 struct lockdep_map dep_map;
48 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
49 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
50 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
51 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
53 /* Include the arch specific part */
54 #include <asm/rwsem.h>
56 /* In all implementations count != 0 means locked */
57 static inline int rwsem_is_locked(struct rw_semaphore *sem)
59 return sem->count != 0;
64 /* Common initializer macros and functions */
66 #ifdef CONFIG_DEBUG_LOCK_ALLOC
67 # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
69 # define __RWSEM_DEP_MAP_INIT(lockname)
72 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
73 #define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL
75 #define __RWSEM_OPT_INIT(lockname)
78 #define __RWSEM_INITIALIZER(name) \
79 { .count = RWSEM_UNLOCKED_VALUE, \
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) }
85 #define DECLARE_RWSEM(name) \
86 struct rw_semaphore name = __RWSEM_INITIALIZER(name)
88 extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
89 struct lock_class_key *key);
91 #define init_rwsem(sem) \
93 static struct lock_class_key __key; \
95 __init_rwsem((sem), #sem, &__key); \
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
104 static inline int rwsem_is_contended(struct rw_semaphore *sem)
106 return !list_empty(&sem->wait_list);
112 extern void down_read(struct rw_semaphore *sem);
115 * trylock for reading -- returns 1 if successful, 0 if contention
117 extern int down_read_trylock(struct rw_semaphore *sem);
122 extern void down_write(struct rw_semaphore *sem);
125 * trylock for writing -- returns 1 if successful, 0 if contention
127 extern int down_write_trylock(struct rw_semaphore *sem);
130 * release a read lock
132 extern void up_read(struct rw_semaphore *sem);
135 * release a write lock
137 extern void up_write(struct rw_semaphore *sem);
140 * downgrade write lock to read lock
142 extern void downgrade_write(struct rw_semaphore *sem);
144 #ifdef CONFIG_DEBUG_LOCK_ALLOC
146 * nested locking. NOTE: rwsems are not allowed to recurse
147 * (which occurs if the same task tries to acquire the same
148 * lock instance multiple times), but multiple locks of the
149 * same lock class might be taken, if the order of the locks
150 * is always the same. This ordering rule can be expressed
151 * to lockdep via the _nested() APIs, but enumerating the
152 * subclasses that are used. (If the nesting relationship is
153 * static then another method for expressing nested locking is
154 * the explicit definition of lock class keys and the use of
155 * lockdep_set_class() at lock initialization time.
156 * See Documentation/locking/lockdep-design.txt for more details.)
158 extern void down_read_nested(struct rw_semaphore *sem, int subclass);
159 extern void down_write_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_read_non_owner(sem) down_read(sem)
181 # define up_read_non_owner(sem) up_read(sem)
184 #endif /* !PREEMPT_RT_FULL */
186 #endif /* _LINUX_RWSEM_H */