/* SPDX-License-Identifier: GPL-2.0 *//* * The owner field of the rw_semaphore structure will be set to * RWSEM_READER_OWNED when a reader grabs the lock. A writer will clear * the owner field when it unlocks. A reader, on the other hand, will * not touch the owner field when it unlocks. * * In essence, the owner field now has the following 4 states: *  1) 0 *     - lock is free or the owner hasn't set the field yet *  2) RWSEM_READER_OWNED *     - lock is currently or previously owned by readers (lock is free *       or not set by owner yet) *  3) RWSEM_ANONYMOUSLY_OWNED bit set with some other bits set as well *     - lock is owned by an anonymous writer, so spinning on the lock *       owner should be disabled. *  4) Other non-zero value *     - a writer owns the lock and other writers can spin on the lock owner. */#define RWSEM_ANONYMOUSLY_OWNED	(1UL << 0)#define RWSEM_READER_OWNED	((struct task_struct *)RWSEM_ANONYMOUSLY_OWNED) #ifdef CONFIG_DEBUG_RWSEMS# define DEBUG_RWSEMS_WARN_ON(c)	DEBUG_LOCKS_WARN_ON(c)#else# define DEBUG_RWSEMS_WARN_ON(c)#endif #ifdef CONFIG_RWSEM_SPIN_ON_OWNER/* * All writes to owner are protected by WRITE_ONCE() to make sure that * store tearing can't happen as optimistic spinners may read and use * the owner value concurrently without lock. Read from owner, however, * may not need READ_ONCE() as long as the pointer value is only used * for comparison and isn't being dereferenced. */static inline void rwsem_set_owner(struct rw_semaphore *sem){	WRITE_ONCE(sem->owner, current);} static inline void rwsem_clear_owner(struct rw_semaphore *sem){	WRITE_ONCE(sem->owner, NULL);} static inline void rwsem_set_reader_owned(struct rw_semaphore *sem){	/*	 * We check the owner value first to make sure that we will only	 * do a write to the rwsem cacheline when it is really necessary	 * to minimize cacheline contention.	 */	if (READ_ONCE(sem->owner) != RWSEM_READER_OWNED)		WRITE_ONCE(sem->owner, RWSEM_READER_OWNED);} /* * Return true if the a rwsem waiter can spin on the rwsem's owner * and steal the lock, i.e. the lock is not anonymously owned. * N.B. !owner is considered spinnable. */static inline bool is_rwsem_owner_spinnable(struct task_struct *owner){	return !((unsigned long)owner & RWSEM_ANONYMOUSLY_OWNED);} /* * Return true if rwsem is owned by an anonymous writer or readers. */static inline bool rwsem_has_anonymous_owner(struct task_struct *owner){	return (unsigned long)owner & RWSEM_ANONYMOUSLY_OWNED;}#elsestatic inline void rwsem_set_owner(struct rw_semaphore *sem){} static inline void rwsem_clear_owner(struct rw_semaphore *sem){} static inline void rwsem_set_reader_owned(struct rw_semaphore *sem){}#endif