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1/*
2 * Queued read/write locks
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P.
15 *
16 * Authors: Waiman Long <waiman.long@hp.com>
17 */
18#include <linux/smp.h>
19#include <linux/bug.h>
20#include <linux/cpumask.h>
21#include <linux/percpu.h>
22#include <linux/hardirq.h>
23#include <linux/spinlock.h>
24#include <asm/qrwlock.h>
25
26/**
27 * queued_read_lock_slowpath - acquire read lock of a queue rwlock
28 * @lock: Pointer to queue rwlock structure
29 */
30void queued_read_lock_slowpath(struct qrwlock *lock)
31{
32 /*
33 * Readers come here when they cannot get the lock without waiting
34 */
35 if (unlikely(in_interrupt())) {
36 /*
37 * Readers in interrupt context will get the lock immediately
38 * if the writer is just waiting (not holding the lock yet),
39 * so spin with ACQUIRE semantics until the lock is available
40 * without waiting in the queue.
41 */
42 atomic_cond_read_acquire(&lock->cnts, !(VAL & _QW_LOCKED));
43 return;
44 }
45 atomic_sub(_QR_BIAS, &lock->cnts);
46
47 /*
48 * Put the reader into the wait queue
49 */
50 arch_spin_lock(&lock->wait_lock);
51 atomic_add(_QR_BIAS, &lock->cnts);
52
53 /*
54 * The ACQUIRE semantics of the following spinning code ensure
55 * that accesses can't leak upwards out of our subsequent critical
56 * section in the case that the lock is currently held for write.
57 */
58 atomic_cond_read_acquire(&lock->cnts, !(VAL & _QW_LOCKED));
59
60 /*
61 * Signal the next one in queue to become queue head
62 */
63 arch_spin_unlock(&lock->wait_lock);
64}
65EXPORT_SYMBOL(queued_read_lock_slowpath);
66
67/**
68 * queued_write_lock_slowpath - acquire write lock of a queue rwlock
69 * @lock : Pointer to queue rwlock structure
70 */
71void queued_write_lock_slowpath(struct qrwlock *lock)
72{
73 /* Put the writer into the wait queue */
74 arch_spin_lock(&lock->wait_lock);
75
76 /* Try to acquire the lock directly if no reader is present */
77 if (!atomic_read(&lock->cnts) &&
78 (atomic_cmpxchg_acquire(&lock->cnts, 0, _QW_LOCKED) == 0))
79 goto unlock;
80
81 /* Set the waiting flag to notify readers that a writer is pending */
82 atomic_add(_QW_WAITING, &lock->cnts);
83
84 /* When no more readers or writers, set the locked flag */
85 do {
86 atomic_cond_read_acquire(&lock->cnts, VAL == _QW_WAITING);
87 } while (atomic_cmpxchg_relaxed(&lock->cnts, _QW_WAITING,
88 _QW_LOCKED) != _QW_WAITING);
89unlock:
90 arch_spin_unlock(&lock->wait_lock);
91}
92EXPORT_SYMBOL(queued_write_lock_slowpath);
1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * Queued read/write locks
4 *
5 * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P.
6 *
7 * Authors: Waiman Long <waiman.long@hp.com>
8 */
9#include <linux/smp.h>
10#include <linux/bug.h>
11#include <linux/cpumask.h>
12#include <linux/percpu.h>
13#include <linux/hardirq.h>
14#include <linux/spinlock.h>
15#include <trace/events/lock.h>
16
17/**
18 * queued_read_lock_slowpath - acquire read lock of a queued rwlock
19 * @lock: Pointer to queued rwlock structure
20 */
21void __lockfunc queued_read_lock_slowpath(struct qrwlock *lock)
22{
23 /*
24 * Readers come here when they cannot get the lock without waiting
25 */
26 if (unlikely(in_interrupt())) {
27 /*
28 * Readers in interrupt context will get the lock immediately
29 * if the writer is just waiting (not holding the lock yet),
30 * so spin with ACQUIRE semantics until the lock is available
31 * without waiting in the queue.
32 */
33 atomic_cond_read_acquire(&lock->cnts, !(VAL & _QW_LOCKED));
34 return;
35 }
36 atomic_sub(_QR_BIAS, &lock->cnts);
37
38 trace_contention_begin(lock, LCB_F_SPIN | LCB_F_READ);
39
40 /*
41 * Put the reader into the wait queue
42 */
43 arch_spin_lock(&lock->wait_lock);
44 atomic_add(_QR_BIAS, &lock->cnts);
45
46 /*
47 * The ACQUIRE semantics of the following spinning code ensure
48 * that accesses can't leak upwards out of our subsequent critical
49 * section in the case that the lock is currently held for write.
50 */
51 atomic_cond_read_acquire(&lock->cnts, !(VAL & _QW_LOCKED));
52
53 /*
54 * Signal the next one in queue to become queue head
55 */
56 arch_spin_unlock(&lock->wait_lock);
57
58 trace_contention_end(lock, 0);
59}
60EXPORT_SYMBOL(queued_read_lock_slowpath);
61
62/**
63 * queued_write_lock_slowpath - acquire write lock of a queued rwlock
64 * @lock : Pointer to queued rwlock structure
65 */
66void __lockfunc queued_write_lock_slowpath(struct qrwlock *lock)
67{
68 int cnts;
69
70 trace_contention_begin(lock, LCB_F_SPIN | LCB_F_WRITE);
71
72 /* Put the writer into the wait queue */
73 arch_spin_lock(&lock->wait_lock);
74
75 /* Try to acquire the lock directly if no reader is present */
76 if (!(cnts = atomic_read(&lock->cnts)) &&
77 atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED))
78 goto unlock;
79
80 /* Set the waiting flag to notify readers that a writer is pending */
81 atomic_or(_QW_WAITING, &lock->cnts);
82
83 /* When no more readers or writers, set the locked flag */
84 do {
85 cnts = atomic_cond_read_relaxed(&lock->cnts, VAL == _QW_WAITING);
86 } while (!atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED));
87unlock:
88 arch_spin_unlock(&lock->wait_lock);
89
90 trace_contention_end(lock, 0);
91}
92EXPORT_SYMBOL(queued_write_lock_slowpath);