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// SPDX-License-Identifier: GPL-2.0/* rwsem-spinlock.c: R/W semaphores: contention handling functions for * generic spinlock implementation * * Copyright (c) 2001 David Howells (dhowells@redhat.com). * - Derived partially from idea by Andrea Arcangeli <andrea@suse.de> * - Derived also from comments by Linus */enum rwsem_waiter_type { RWSEM_WAITING_FOR_WRITE, RWSEM_WAITING_FOR_READ};struct rwsem_waiter { struct list_head list; struct task_struct *task; enum rwsem_waiter_type type;};int rwsem_is_locked(struct rw_semaphore *sem){ int ret = 1; unsigned long flags; if (raw_spin_trylock_irqsave(&sem->wait_lock, flags)) { ret = (sem->count != 0); raw_spin_unlock_irqrestore(&sem->wait_lock, flags); } return ret;}EXPORT_SYMBOL(rwsem_is_locked);/* * initialise the semaphore */void __init_rwsem(struct rw_semaphore *sem, const char *name, struct lock_class_key *key){ /* * Make sure we are not reinitializing a held semaphore: */ debug_check_no_locks_freed((void *)sem, sizeof(*sem)); lockdep_init_map(&sem->dep_map, name, key, 0); sem->count = 0; raw_spin_lock_init(&sem->wait_lock); INIT_LIST_HEAD(&sem->wait_list);}EXPORT_SYMBOL(__init_rwsem);/* * handle the lock release when processes blocked on it that can now run * - if we come here, then: * - the 'active count' _reached_ zero * - the 'waiting count' is non-zero * - the spinlock must be held by the caller * - woken process blocks are discarded from the list after having task zeroed * - writers are only woken if wakewrite is non-zero */static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem, int wakewrite){ struct rwsem_waiter *waiter; struct task_struct *tsk; int woken; waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); if (waiter->type == RWSEM_WAITING_FOR_WRITE) { if (wakewrite) /* Wake up a writer. Note that we do not grant it the * lock - it will have to acquire it when it runs. */ wake_up_process(waiter->task); goto out; } /* grant an infinite number of read locks to the front of the queue */ woken = 0; do { struct list_head *next = waiter->list.next; list_del(&waiter->list); tsk = waiter->task; /* * Make sure we do not wakeup the next reader before * setting the nil condition to grant the next reader;