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Diffstat (limited to 'include/linux/rwsem.h')
| -rw-r--r-- | include/linux/rwsem.h | 261 |
1 files changed, 261 insertions, 0 deletions
diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h new file mode 100644 index 000000000..1dd530ce8 --- /dev/null +++ b/include/linux/rwsem.h @@ -0,0 +1,261 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* 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/list.h> +#include <linux/spinlock.h> +#include <linux/atomic.h> +#include <linux/err.h> +#include <linux/cleanup.h> + +#ifdef CONFIG_DEBUG_LOCK_ALLOC +# define __RWSEM_DEP_MAP_INIT(lockname) \ + .dep_map = { \ + .name = #lockname, \ + .wait_type_inner = LD_WAIT_SLEEP, \ + }, +#else +# define __RWSEM_DEP_MAP_INIT(lockname) +#endif + +#ifndef CONFIG_PREEMPT_RT + +#ifdef CONFIG_RWSEM_SPIN_ON_OWNER +#include <linux/osq_lock.h> +#endif + +/* + * For an uncontended rwsem, count and owner are the only fields a task + * needs to touch when acquiring the rwsem. So they are put next to each + * other to increase the chance that they will share the same cacheline. + * + * In a contended rwsem, the owner is likely the most frequently accessed + * field in the structure as the optimistic waiter that holds the osq lock + * will spin on owner. For an embedded rwsem, other hot fields in the + * containing structure should be moved further away from the rwsem to + * reduce the chance that they will share the same cacheline causing + * cacheline bouncing problem. + */ +struct rw_semaphore { + atomic_long_t count; + /* + * Write owner or one of the read owners as well flags regarding + * the current state of the rwsem. Can be used as a speculative + * check to see if the write owner is running on the cpu. + */ + atomic_long_t owner; +#ifdef CONFIG_RWSEM_SPIN_ON_OWNER + struct optimistic_spin_queue osq; /* spinner MCS lock */ +#endif + raw_spinlock_t wait_lock; + struct list_head wait_list; +#ifdef CONFIG_DEBUG_RWSEMS + void *magic; +#endif +#ifdef CONFIG_DEBUG_LOCK_ALLOC + struct lockdep_map dep_map; +#endif +}; + +/* In all implementations count != 0 means locked */ +static inline int rwsem_is_locked(struct rw_semaphore *sem) +{ + return atomic_long_read(&sem->count) != 0; +} + +#define RWSEM_UNLOCKED_VALUE 0L +#define __RWSEM_COUNT_INIT(name) .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE) + +/* Common initializer macros and functions */ + +#ifdef CONFIG_DEBUG_RWSEMS +# define __RWSEM_DEBUG_INIT(lockname) .magic = &lockname, +#else +# define __RWSEM_DEBUG_INIT(lockname) +#endif + +#ifdef CONFIG_RWSEM_SPIN_ON_OWNER +#define __RWSEM_OPT_INIT(lockname) .osq = OSQ_LOCK_UNLOCKED, +#else +#define __RWSEM_OPT_INIT(lockname) +#endif + +#define __RWSEM_INITIALIZER(name) \ + { __RWSEM_COUNT_INIT(name), \ + .owner = ATOMIC_LONG_INIT(0), \ + __RWSEM_OPT_INIT(name) \ + .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock),\ + .wait_list = LIST_HEAD_INIT((name).wait_list), \ + __RWSEM_DEBUG_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 already 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); +} + +#else /* !CONFIG_PREEMPT_RT */ + +#include <linux/rwbase_rt.h> + +struct rw_semaphore { + struct rwbase_rt rwbase; +#ifdef CONFIG_DEBUG_LOCK_ALLOC + struct lockdep_map dep_map; +#endif +}; + +#define __RWSEM_INITIALIZER(name) \ + { \ + .rwbase = __RWBASE_INITIALIZER(name), \ + __RWSEM_DEP_MAP_INIT(name) \ + } + +#define DECLARE_RWSEM(lockname) \ + struct rw_semaphore lockname = __RWSEM_INITIALIZER(lockname) + +extern void __init_rwsem(struct rw_semaphore *rwsem, 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) + +static __always_inline int rwsem_is_locked(struct rw_semaphore *sem) +{ + return rw_base_is_locked(&sem->rwbase); +} + +static __always_inline int rwsem_is_contended(struct rw_semaphore *sem) +{ + return rw_base_is_contended(&sem->rwbase); +} + +#endif /* CONFIG_PREEMPT_RT */ + +/* + * The functions below are the same for all rwsem implementations including + * the RT specific variant. + */ + +/* + * lock for reading + */ +extern void down_read(struct rw_semaphore *sem); +extern int __must_check down_read_interruptible(struct rw_semaphore *sem); +extern int __must_check down_read_killable(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); +extern int __must_check down_write_killable(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); + +DEFINE_GUARD(rwsem_read, struct rw_semaphore *, down_read(_T), up_read(_T)) +DEFINE_GUARD(rwsem_write, struct rw_semaphore *, down_write(_T), up_write(_T)) + +DEFINE_FREE(up_read, struct rw_semaphore *, if (_T) up_read(_T)) +DEFINE_FREE(up_write, struct rw_semaphore *, if (_T) up_write(_T)) + + +/* + * 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.rst for more details.) + */ +extern void down_read_nested(struct rw_semaphore *sem, int subclass); +extern int __must_check down_read_killable_nested(struct rw_semaphore *sem, int subclass); +extern void down_write_nested(struct rw_semaphore *sem, int subclass); +extern int down_write_killable_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_read_killable_nested(sem, subclass) down_read_killable(sem) +# define down_write_nest_lock(sem, nest_lock) down_write(sem) +# define down_write_nested(sem, subclass) down_write(sem) +# define down_write_killable_nested(sem, subclass) down_write_killable(sem) +# define down_read_non_owner(sem) down_read(sem) +# define up_read_non_owner(sem) up_read(sem) +#endif + +#endif /* _LINUX_RWSEM_H */ |