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c942fddf | 1 | // SPDX-License-Identifier: GPL-2.0-or-later |
70af2f8a | 2 | /* |
c7114b4e | 3 | * Queued read/write locks |
70af2f8a | 4 | * |
70af2f8a WL |
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> | |
9ab6055f | 14 | #include <linux/spinlock.h> |
70af2f8a WL |
15 | #include <asm/qrwlock.h> |
16 | ||
70af2f8a | 17 | /** |
f7d71f20 | 18 | * queued_read_lock_slowpath - acquire read lock of a queue rwlock |
70af2f8a WL |
19 | * @lock: Pointer to queue rwlock structure |
20 | */ | |
b519b56e | 21 | void queued_read_lock_slowpath(struct qrwlock *lock) |
70af2f8a | 22 | { |
70af2f8a WL |
23 | /* |
24 | * Readers come here when they cannot get the lock without waiting | |
25 | */ | |
26 | if (unlikely(in_interrupt())) { | |
27 | /* | |
0e06e5be | 28 | * Readers in interrupt context will get the lock immediately |
b519b56e WD |
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. | |
70af2f8a | 32 | */ |
d1331661 | 33 | atomic_cond_read_acquire(&lock->cnts, !(VAL & _QW_LOCKED)); |
70af2f8a WL |
34 | return; |
35 | } | |
36 | atomic_sub(_QR_BIAS, &lock->cnts); | |
37 | ||
38 | /* | |
39 | * Put the reader into the wait queue | |
40 | */ | |
6e1e5196 | 41 | arch_spin_lock(&lock->wait_lock); |
b519b56e | 42 | atomic_add(_QR_BIAS, &lock->cnts); |
70af2f8a WL |
43 | |
44 | /* | |
77e430e3 WD |
45 | * The ACQUIRE semantics of the following spinning code ensure |
46 | * that accesses can't leak upwards out of our subsequent critical | |
47 | * section in the case that the lock is currently held for write. | |
70af2f8a | 48 | */ |
d1331661 | 49 | atomic_cond_read_acquire(&lock->cnts, !(VAL & _QW_LOCKED)); |
70af2f8a WL |
50 | |
51 | /* | |
52 | * Signal the next one in queue to become queue head | |
53 | */ | |
6e1e5196 | 54 | arch_spin_unlock(&lock->wait_lock); |
70af2f8a | 55 | } |
f7d71f20 | 56 | EXPORT_SYMBOL(queued_read_lock_slowpath); |
70af2f8a WL |
57 | |
58 | /** | |
f7d71f20 | 59 | * queued_write_lock_slowpath - acquire write lock of a queue rwlock |
70af2f8a WL |
60 | * @lock : Pointer to queue rwlock structure |
61 | */ | |
f7d71f20 | 62 | void queued_write_lock_slowpath(struct qrwlock *lock) |
70af2f8a | 63 | { |
70af2f8a | 64 | /* Put the writer into the wait queue */ |
6e1e5196 | 65 | arch_spin_lock(&lock->wait_lock); |
70af2f8a WL |
66 | |
67 | /* Try to acquire the lock directly if no reader is present */ | |
68 | if (!atomic_read(&lock->cnts) && | |
77e430e3 | 69 | (atomic_cmpxchg_acquire(&lock->cnts, 0, _QW_LOCKED) == 0)) |
70af2f8a WL |
70 | goto unlock; |
71 | ||
d1331661 WD |
72 | /* Set the waiting flag to notify readers that a writer is pending */ |
73 | atomic_add(_QW_WAITING, &lock->cnts); | |
70af2f8a | 74 | |
d1331661 | 75 | /* When no more readers or writers, set the locked flag */ |
b519b56e WD |
76 | do { |
77 | atomic_cond_read_acquire(&lock->cnts, VAL == _QW_WAITING); | |
78 | } while (atomic_cmpxchg_relaxed(&lock->cnts, _QW_WAITING, | |
79 | _QW_LOCKED) != _QW_WAITING); | |
70af2f8a | 80 | unlock: |
6e1e5196 | 81 | arch_spin_unlock(&lock->wait_lock); |
70af2f8a | 82 | } |
f7d71f20 | 83 | EXPORT_SYMBOL(queued_write_lock_slowpath); |