v4.19.13 snapshot.
diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c
new file mode 100644
index 0000000..c7471c3
--- /dev/null
+++ b/kernel/locking/qrwlock.c
@@ -0,0 +1,92 @@
+/*
+ * Queued read/write locks
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * (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)
+{
+ /* 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 {
+ atomic_cond_read_acquire(&lock->cnts, VAL == _QW_WAITING);
+ } while (atomic_cmpxchg_relaxed(&lock->cnts, _QW_WAITING,
+ _QW_LOCKED) != _QW_WAITING);
+unlock:
+ arch_spin_unlock(&lock->wait_lock);
+}
+EXPORT_SYMBOL(queued_write_lock_slowpath);