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