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-rw-r--r--kernel/locking/qrwlock.c84
1 files changed, 84 insertions, 0 deletions
diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c
new file mode 100644
index 000000000..909b0bf22
--- /dev/null
+++ b/kernel/locking/qrwlock.c
@@ -0,0 +1,84 @@
+// 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 <asm/qrwlock.h>
+
+/**
+ * queued_read_lock_slowpath - acquire read lock of a queue rwlock
+ * @lock: Pointer to queue rwlock structure
+ */
+void 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);
+
+ /*
+ * 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);
+}
+EXPORT_SYMBOL(queued_read_lock_slowpath);
+
+/**
+ * queued_write_lock_slowpath - acquire write lock of a queue rwlock
+ * @lock : Pointer to queue rwlock structure
+ */
+void queued_write_lock_slowpath(struct qrwlock *lock)
+{
+ int cnts;
+
+ /* 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 (!atomic_read(&lock->cnts) &&
+ (atomic_cmpxchg_acquire(&lock->cnts, 0, _QW_LOCKED) == 0))
+ goto unlock;
+
+ /* Set the waiting flag to notify readers that a writer is pending */
+ atomic_add(_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);
+}
+EXPORT_SYMBOL(queued_write_lock_slowpath);