diff options
Diffstat (limited to 'kernel/include/linux/rwsem.h')
| -rw-r--r-- | kernel/include/linux/rwsem.h | 186 |
1 files changed, 186 insertions, 0 deletions
diff --git a/kernel/include/linux/rwsem.h b/kernel/include/linux/rwsem.h new file mode 100644 index 000000000..2b2148431 --- /dev/null +++ b/kernel/include/linux/rwsem.h @@ -0,0 +1,186 @@ +/* rwsem.h: R/W semaphores, public interface + * + * Written by David Howells (dhowells@redhat.com). + * Derived from asm-i386/semaphore.h + */ + +#ifndef _LINUX_RWSEM_H +#define _LINUX_RWSEM_H + +#include <linux/linkage.h> + +#include <linux/types.h> +#include <linux/kernel.h> +#include <linux/list.h> +#include <linux/spinlock.h> +#include <linux/atomic.h> +#ifdef CONFIG_RWSEM_SPIN_ON_OWNER +#include <linux/osq_lock.h> +#endif + +#ifdef CONFIG_PREEMPT_RT_FULL +#include <linux/rwsem_rt.h> +#else /* PREEMPT_RT_FULL */ + +struct rw_semaphore; + +#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK +#include <linux/rwsem-spinlock.h> /* use a generic implementation */ +#else +/* All arch specific implementations share the same struct */ +struct rw_semaphore { + long count; + struct list_head wait_list; + raw_spinlock_t wait_lock; +#ifdef CONFIG_RWSEM_SPIN_ON_OWNER + struct optimistic_spin_queue osq; /* spinner MCS lock */ + /* + * Write owner. Used as a speculative check to see + * if the owner is running on the cpu. + */ + struct task_struct *owner; +#endif +#ifdef CONFIG_DEBUG_LOCK_ALLOC + struct lockdep_map dep_map; +#endif +}; + +extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem); +extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem); +extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *); +extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem); + +/* Include the arch specific part */ +#include <asm/rwsem.h> + +/* In all implementations count != 0 means locked */ +static inline int rwsem_is_locked(struct rw_semaphore *sem) +{ + return sem->count != 0; +} + +#endif + +/* Common initializer macros and functions */ + +#ifdef CONFIG_DEBUG_LOCK_ALLOC +# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname } +#else +# define __RWSEM_DEP_MAP_INIT(lockname) +#endif + +#ifdef CONFIG_RWSEM_SPIN_ON_OWNER +#define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL +#else +#define __RWSEM_OPT_INIT(lockname) +#endif + +#define __RWSEM_INITIALIZER(name) \ + { .count = RWSEM_UNLOCKED_VALUE, \ + .wait_list = LIST_HEAD_INIT((name).wait_list), \ + .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \ + __RWSEM_OPT_INIT(name) \ + __RWSEM_DEP_MAP_INIT(name) } + +#define DECLARE_RWSEM(name) \ + struct rw_semaphore name = __RWSEM_INITIALIZER(name) + +extern void __init_rwsem(struct rw_semaphore *sem, const char *name, + struct lock_class_key *key); + +#define init_rwsem(sem) \ +do { \ + static struct lock_class_key __key; \ + \ + __init_rwsem((sem), #sem, &__key); \ +} while (0) + +/* + * This is the same regardless of which rwsem implementation that is being used. + * It is just a heuristic meant to be called by somebody alreadying holding the + * rwsem to see if somebody from an incompatible type is wanting access to the + * lock. + */ +static inline int rwsem_is_contended(struct rw_semaphore *sem) +{ + return !list_empty(&sem->wait_list); +} + +/* + * lock for reading + */ +extern void down_read(struct rw_semaphore *sem); + +/* + * trylock for reading -- returns 1 if successful, 0 if contention + */ +extern int down_read_trylock(struct rw_semaphore *sem); + +/* + * lock for writing + */ +extern void down_write(struct rw_semaphore *sem); + +/* + * trylock for writing -- returns 1 if successful, 0 if contention + */ +extern int down_write_trylock(struct rw_semaphore *sem); + +/* + * release a read lock + */ +extern void up_read(struct rw_semaphore *sem); + +/* + * release a write lock + */ +extern void up_write(struct rw_semaphore *sem); + +/* + * downgrade write lock to read lock + */ +extern void downgrade_write(struct rw_semaphore *sem); + +#ifdef CONFIG_DEBUG_LOCK_ALLOC +/* + * nested locking. NOTE: rwsems are not allowed to recurse + * (which occurs if the same task tries to acquire the same + * lock instance multiple times), but multiple locks of the + * same lock class might be taken, if the order of the locks + * is always the same. This ordering rule can be expressed + * to lockdep via the _nested() APIs, but enumerating the + * subclasses that are used. (If the nesting relationship is + * static then another method for expressing nested locking is + * the explicit definition of lock class keys and the use of + * lockdep_set_class() at lock initialization time. + * See Documentation/locking/lockdep-design.txt for more details.) + */ +extern void down_read_nested(struct rw_semaphore *sem, int subclass); +extern void down_write_nested(struct rw_semaphore *sem, int subclass); +extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock); + +# define down_write_nest_lock(sem, nest_lock) \ +do { \ + typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \ + _down_write_nest_lock(sem, &(nest_lock)->dep_map); \ +} while (0); + +/* + * Take/release a lock when not the owner will release it. + * + * [ This API should be avoided as much as possible - the + * proper abstraction for this case is completions. ] + */ +extern void down_read_non_owner(struct rw_semaphore *sem); +extern void up_read_non_owner(struct rw_semaphore *sem); +#else +# define down_read_nested(sem, subclass) down_read(sem) +# define down_write_nest_lock(sem, nest_lock) down_write(sem) +# define down_write_nested(sem, subclass) down_write(sem) +# define down_read_non_owner(sem) down_read(sem) +# define up_read_non_owner(sem) up_read(sem) +#endif + +#endif /* !PREEMPT_RT_FULL */ + +#endif /* _LINUX_RWSEM_H */ |