include/linux/rwsem.h

   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 #ifdef CONFIG_PREEMPT_RT
  13 # include <linux/rt_lock.h>
  14 #endif
  15
  16 #include <linux/types.h>
  17 #include <linux/kernel.h>
  18 #include <asm/system.h>
  19 #include <asm/atomic.h>
  20
  21 #ifndef CONFIG_PREEMPT_RT
  22 /*
  23  * On !PREEMPT_RT all rw-semaphores are compat:
  24  */
  25 #define compat_rw_semaphore rw_semaphore
  26 #endif
  27
  28 struct compat_rw_semaphore;
  29
  30 #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
  31 # include <linux/rwsem-spinlock.h> /* use a generic implementation */
  32 #  ifndef CONFIG_PREEMPT_RT
  33 #  define __RWSEM_INITIALIZER __COMPAT_RWSEM_INITIALIZER
  34 #  define DECLARE_RWSEM COMPAT_DECLARE_RWSEM
  35 # endif
  36 #else
  37 # include <asm/rwsem.h> /* use an arch-specific implementation */
  38 #endif
  39
  40 /*
  41  * lock for reading
  42  */
  43 extern void compat_down_read(struct compat_rw_semaphore *sem);
  44
  45 /*
  46  * trylock for reading -- returns 1 if successful, 0 if contention
  47  */
  48 extern int compat_down_read_trylock(struct compat_rw_semaphore *sem);
  49
  50 /*
  51  * lock for writing
  52  */
  53 extern void compat_down_write(struct compat_rw_semaphore *sem);
  54
  55 /*
  56  * trylock for writing -- returns 1 if successful, 0 if contention
  57  */
  58 extern int compat_down_write_trylock(struct compat_rw_semaphore *sem);
  59
  60 /*
  61  * release a read lock
  62  */
  63 extern void compat_up_read(struct compat_rw_semaphore *sem);
  64
  65 /*
  66  * release a write lock
  67  */
  68 extern void compat_up_write(struct compat_rw_semaphore *sem);
  69
  70 /*
  71  * downgrade write lock to read lock
  72  */
  73 extern void compat_downgrade_write(struct compat_rw_semaphore *sem);
  74
  75 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  76 /*
  77  * nested locking. NOTE: rwsems are not allowed to recurse
  78  * (which occurs if the same task tries to acquire the same
  79  * lock instance multiple times), but multiple locks of the
  80  * same lock class might be taken, if the order of the locks
  81  * is always the same. This ordering rule can be expressed
  82  * to lockdep via the _nested() APIs, but enumerating the
  83  * subclasses that are used. (If the nesting relationship is
  84  * static then another method for expressing nested locking is
  85  * the explicit definition of lock class keys and the use of
  86  * lockdep_set_class() at lock initialization time.
  87  * See Documentation/lockdep-design.txt for more details.)
  88  */
  89 extern void
  90 compat_down_read_nested(struct compat_rw_semaphore *sem, int subclass);
  91 extern void
  92 compat_down_write_nested(struct compat_rw_semaphore *sem, int subclass);
  93 /*
  94  * Take/release a lock when not the owner will release it.
  95  *
  96  * [ This API should be avoided as much as possible - the
  97  *   proper abstraction for this case is completions. ]
  98  */
  99 extern void
 100 compat_down_read_non_owner(struct compat_rw_semaphore *sem);
 101 extern void
 102 compat_up_read_non_owner(struct compat_rw_semaphore *sem);
 103 #else
 104 # define compat_down_read_nested(sem, subclass)         compat_down_read(sem)
 105 # define compat_down_write_nested(sem, subclass)        compat_down_write(sem)
 106 # define compat_down_read_non_owner(sem)                compat_down_read(sem)
 107 # define compat_up_read_non_owner(sem)                  compat_up_read(sem)
 108 #endif
 109
 110 #ifndef CONFIG_PREEMPT_RT
 111
 112 #define DECLARE_RWSEM COMPAT_DECLARE_RWSEM
 113
 114 /*
 115  * NOTE, lockdep: this has to be a macro, so that separate class-keys
 116  * get generated by the compiler, if the same function does multiple
 117  * init_rwsem() calls to different rwsems.
 118  */
 119 #define init_rwsem(rwsem)       compat_init_rwsem(rwsem)
 120
 121 static inline void down_read(struct compat_rw_semaphore *rwsem)
 122 {
 123         compat_down_read(rwsem);
 124 }
 125 static inline int down_read_trylock(struct compat_rw_semaphore *rwsem)
 126 {
 127         return compat_down_read_trylock(rwsem);
 128 }
 129 static inline void down_write(struct compat_rw_semaphore *rwsem)
 130 {
 131         compat_down_write(rwsem);
 132 }
 133 static inline int down_write_trylock(struct compat_rw_semaphore *rwsem)
 134 {
 135         return compat_down_write_trylock(rwsem);
 136 }
 137 static inline void up_read(struct compat_rw_semaphore *rwsem)
 138 {
 139         compat_up_read(rwsem);
 140 }
 141 static inline void up_write(struct compat_rw_semaphore *rwsem)
 142 {
 143         compat_up_write(rwsem);
 144 }
 145 static inline void downgrade_write(struct compat_rw_semaphore *rwsem)
 146 {
 147         compat_downgrade_write(rwsem);
 148 }
 149 static inline int rwsem_is_locked(struct compat_rw_semaphore *sem)
 150 {
 151         return compat_rwsem_is_locked(sem);
 152 }
 153 # define down_read_nested(sem, subclass) \
 154                 compat_down_read_nested(sem, subclass)
 155 # define down_write_nested(sem, subclass) \
 156                 compat_down_write_nested(sem, subclass)
 157 # define down_read_non_owner(sem) \
 158                 compat_down_read_non_owner(sem)
 159 # define up_read_non_owner(sem) \
 160                 compat_up_read_non_owner(sem)
 161 #endif /* !CONFIG_PREEMPT_RT */
 162
 163 #endif /* _LINUX_RWSEM_H */