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

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  1 /* SPDX-License-Identifier: GPL-2.0 */
  2 /* rwsem.h: R/W semaphores, public interface
  3  *
  4  * Written by David Howells (dhowells@redhat.com).
  5  * Derived from asm-i386/semaphore.h
  6  */
  7 
  8 #ifndef _LINUX_RWSEM_H
  9 #define _LINUX_RWSEM_H
 10 
 11 #include <linux/linkage.h>
 12 
 13 #include <linux/types.h>
 14 #include <linux/kernel.h>
 15 #include <linux/list.h>
 16 #include <linux/spinlock.h>
 17 #include <linux/atomic.h>
 18 #include <linux/err.h>
 19 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
 20 #include <linux/osq_lock.h>
 21 #endif
 22 
 23 struct rw_semaphore;
 24 
 25 #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
 26 #include <linux/rwsem-spinlock.h> /* use a generic implementation */
 27 #define __RWSEM_INIT_COUNT(name)        .count = RWSEM_UNLOCKED_VALUE
 28 #else
 29 /* All arch specific implementations share the same struct */
 30 struct rw_semaphore {
 31         atomic_long_t count;
 32         struct list_head wait_list;
 33         raw_spinlock_t wait_lock;
 34 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
 35         struct optimistic_spin_queue osq; /* spinner MCS lock */
 36         /*
 37          * Write owner. Used as a speculative check to see
 38          * if the owner is running on the cpu.
 39          */
 40         struct task_struct *owner;
 41 #endif
 42 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 43         struct lockdep_map      dep_map;
 44 #endif
 45 };
 46 
 47 /*
 48  * Setting bit 1 of the owner field but not bit 0 will indicate
 49  * that the rwsem is writer-owned with an unknown owner.
 50  */
 51 #define RWSEM_OWNER_UNKNOWN     ((struct task_struct *)-2L)
 52 
 53 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
 54 extern struct rw_semaphore *rwsem_down_read_failed_killable(struct rw_semaphore *sem);
 55 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
 56 extern struct rw_semaphore *rwsem_down_write_failed_killable(struct rw_semaphore *sem);
 57 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
 58 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
 59 
 60 /* Include the arch specific part */
 61 #include <asm/rwsem.h>
 62 
 63 /* In all implementations count != 0 means locked */
 64 static inline int rwsem_is_locked(struct rw_semaphore *sem)
 65 {
 66         return atomic_long_read(&sem->count) != 0;
 67 }
 68 
 69 #define __RWSEM_INIT_COUNT(name)        .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE)
 70 #endif
 71 
 72 /* Common initializer macros and functions */
 73 
 74 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 75 # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
 76 #else
 77 # define __RWSEM_DEP_MAP_INIT(lockname)
 78 #endif
 79 
 80 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
 81 #define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL
 82 #else
 83 #define __RWSEM_OPT_INIT(lockname)
 84 #endif
 85 
 86 #define __RWSEM_INITIALIZER(name)                               \
 87         { __RWSEM_INIT_COUNT(name),                             \
 88           .wait_list = LIST_HEAD_INIT((name).wait_list),        \
 89           .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \
 90           __RWSEM_OPT_INIT(name)                                \
 91           __RWSEM_DEP_MAP_INIT(name) }
 92 
 93 #define DECLARE_RWSEM(name) \
 94         struct rw_semaphore name = __RWSEM_INITIALIZER(name)
 95 
 96 extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
 97                          struct lock_class_key *key);
 98 
 99 #define init_rwsem(sem)                                         \
100 do {                                                            \
101         static struct lock_class_key __key;                     \
102                                                                 \
103         __init_rwsem((sem), #sem, &__key);                      \
104 } while (0)
105 
106 /*
107  * This is the same regardless of which rwsem implementation that is being used.
108  * It is just a heuristic meant to be called by somebody alreadying holding the
109  * rwsem to see if somebody from an incompatible type is wanting access to the
110  * lock.
111  */
112 static inline int rwsem_is_contended(struct rw_semaphore *sem)
113 {
114         return !list_empty(&sem->wait_list);
115 }
116 
117 /*
118  * lock for reading
119  */
120 extern void down_read(struct rw_semaphore *sem);
121 extern int __must_check down_read_killable(struct rw_semaphore *sem);
122 
123 /*
124  * trylock for reading -- returns 1 if successful, 0 if contention
125  */
126 extern int down_read_trylock(struct rw_semaphore *sem);
127 
128 /*
129  * lock for writing
130  */
131 extern void down_write(struct rw_semaphore *sem);
132 extern int __must_check down_write_killable(struct rw_semaphore *sem);
133 
134 /*
135  * trylock for writing -- returns 1 if successful, 0 if contention
136  */
137 extern int down_write_trylock(struct rw_semaphore *sem);
138 
139 /*
140  * release a read lock
141  */
142 extern void up_read(struct rw_semaphore *sem);
143 
144 /*
145  * release a write lock
146  */
147 extern void up_write(struct rw_semaphore *sem);
148 
149 /*
150  * downgrade write lock to read lock
151  */
152 extern void downgrade_write(struct rw_semaphore *sem);
153 
154 #ifdef CONFIG_DEBUG_LOCK_ALLOC
155 /*
156  * nested locking. NOTE: rwsems are not allowed to recurse
157  * (which occurs if the same task tries to acquire the same
158  * lock instance multiple times), but multiple locks of the
159  * same lock class might be taken, if the order of the locks
160  * is always the same. This ordering rule can be expressed
161  * to lockdep via the _nested() APIs, but enumerating the
162  * subclasses that are used. (If the nesting relationship is
163  * static then another method for expressing nested locking is
164  * the explicit definition of lock class keys and the use of
165  * lockdep_set_class() at lock initialization time.
166  * See Documentation/locking/lockdep-design.txt for more details.)
167  */
168 extern void down_read_nested(struct rw_semaphore *sem, int subclass);
169 extern void down_write_nested(struct rw_semaphore *sem, int subclass);
170 extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass);
171 extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock);
172 
173 # define down_write_nest_lock(sem, nest_lock)                   \
174 do {                                                            \
175         typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
176         _down_write_nest_lock(sem, &(nest_lock)->dep_map);      \
177 } while (0);
178 
179 /*
180  * Take/release a lock when not the owner will release it.
181  *
182  * [ This API should be avoided as much as possible - the
183  *   proper abstraction for this case is completions. ]
184  */
185 extern void down_read_non_owner(struct rw_semaphore *sem);
186 extern void up_read_non_owner(struct rw_semaphore *sem);
187 #else
188 # define down_read_nested(sem, subclass)                down_read(sem)
189 # define down_write_nest_lock(sem, nest_lock)   down_write(sem)
190 # define down_write_nested(sem, subclass)       down_write(sem)
191 # define down_write_killable_nested(sem, subclass)      down_write_killable(sem)
192 # define down_read_non_owner(sem)               down_read(sem)
193 # define up_read_non_owner(sem)                 up_read(sem)
194 #endif
195 
196 #endif /* _LINUX_RWSEM_H */
197 

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