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Diffstat (limited to '')
-rw-r--r-- | kernel/locking/qrwlock.c | 92 |
1 files changed, 92 insertions, 0 deletions
diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c new file mode 100644 index 000000000..d2ef312a8 --- /dev/null +++ b/kernel/locking/qrwlock.c @@ -0,0 +1,92 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Queued read/write locks + * + * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P. + * + * Authors: Waiman Long <waiman.long@hp.com> + */ +#include <linux/smp.h> +#include <linux/bug.h> +#include <linux/cpumask.h> +#include <linux/percpu.h> +#include <linux/hardirq.h> +#include <linux/spinlock.h> +#include <trace/events/lock.h> + +/** + * queued_read_lock_slowpath - acquire read lock of a queued rwlock + * @lock: Pointer to queued rwlock structure + */ +void __lockfunc queued_read_lock_slowpath(struct qrwlock *lock) +{ + /* + * Readers come here when they cannot get the lock without waiting + */ + if (unlikely(in_interrupt())) { + /* + * Readers in interrupt context will get the lock immediately + * if the writer is just waiting (not holding the lock yet), + * so spin with ACQUIRE semantics until the lock is available + * without waiting in the queue. + */ + atomic_cond_read_acquire(&lock->cnts, !(VAL & _QW_LOCKED)); + return; + } + atomic_sub(_QR_BIAS, &lock->cnts); + + trace_contention_begin(lock, LCB_F_SPIN | LCB_F_READ); + + /* + * Put the reader into the wait queue + */ + arch_spin_lock(&lock->wait_lock); + atomic_add(_QR_BIAS, &lock->cnts); + + /* + * The ACQUIRE semantics of the following spinning code ensure + * that accesses can't leak upwards out of our subsequent critical + * section in the case that the lock is currently held for write. + */ + atomic_cond_read_acquire(&lock->cnts, !(VAL & _QW_LOCKED)); + + /* + * Signal the next one in queue to become queue head + */ + arch_spin_unlock(&lock->wait_lock); + + trace_contention_end(lock, 0); +} +EXPORT_SYMBOL(queued_read_lock_slowpath); + +/** + * queued_write_lock_slowpath - acquire write lock of a queued rwlock + * @lock : Pointer to queued rwlock structure + */ +void __lockfunc queued_write_lock_slowpath(struct qrwlock *lock) +{ + int cnts; + + trace_contention_begin(lock, LCB_F_SPIN | LCB_F_WRITE); + + /* Put the writer into the wait queue */ + arch_spin_lock(&lock->wait_lock); + + /* Try to acquire the lock directly if no reader is present */ + if (!(cnts = atomic_read(&lock->cnts)) && + atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED)) + goto unlock; + + /* Set the waiting flag to notify readers that a writer is pending */ + atomic_or(_QW_WAITING, &lock->cnts); + + /* When no more readers or writers, set the locked flag */ + do { + cnts = atomic_cond_read_relaxed(&lock->cnts, VAL == _QW_WAITING); + } while (!atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED)); +unlock: + arch_spin_unlock(&lock->wait_lock); + + trace_contention_end(lock, 0); +} +EXPORT_SYMBOL(queued_write_lock_slowpath); |