| /* 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> |
| |
| #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); |
| |
| /* |
| * 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 */ |