tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
1/*
2 * Copyright 2011 Tilera Corporation. All Rights Reserved.
3 *
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public License
6 * as published by the Free Software Foundation, version 2.
7 *
8 * This program is distributed in the hope that it will be useful, but
9 * WITHOUT ANY WARRANTY; without even the implied warranty of
10 * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
11 * NON INFRINGEMENT. See the GNU General Public License for
12 * more details.
13 */
14
15#include <linux/spinlock.h>
16#include <linux/module.h>
17#include <asm/processor.h>
18
19#include "spinlock_common.h"
20
21/*
22 * Read the spinlock value without allocating in our cache and without
23 * causing an invalidation to another cpu with a copy of the cacheline.
24 * This is important when we are spinning waiting for the lock.
25 */
26static inline u32 arch_spin_read_noalloc(void *lock)
27{
28 return atomic_cmpxchg((atomic_t *)lock, -1, -1);
29}
30
31/*
32 * Wait until the high bits (current) match my ticket.
33 * If we notice the overflow bit set on entry, we clear it.
34 */
35void arch_spin_lock_slow(arch_spinlock_t *lock, u32 my_ticket)
36{
37 if (unlikely(my_ticket & __ARCH_SPIN_NEXT_OVERFLOW)) {
38 __insn_fetchand4(&lock->lock, ~__ARCH_SPIN_NEXT_OVERFLOW);
39 my_ticket &= ~__ARCH_SPIN_NEXT_OVERFLOW;
40 }
41
42 for (;;) {
43 u32 val = arch_spin_read_noalloc(lock);
44 u32 delta = my_ticket - arch_spin_current(val);
45 if (delta == 0)
46 return;
47 relax((128 / CYCLES_PER_RELAX_LOOP) * delta);
48 }
49}
50EXPORT_SYMBOL(arch_spin_lock_slow);
51
52/*
53 * Check the lock to see if it is plausible, and try to get it with cmpxchg().
54 */
55int arch_spin_trylock(arch_spinlock_t *lock)
56{
57 u32 val = arch_spin_read_noalloc(lock);
58 if (unlikely(arch_spin_current(val) != arch_spin_next(val)))
59 return 0;
60 return cmpxchg(&lock->lock, val, (val + 1) & ~__ARCH_SPIN_NEXT_OVERFLOW)
61 == val;
62}
63EXPORT_SYMBOL(arch_spin_trylock);
64
65
66/*
67 * If the read lock fails due to a writer, we retry periodically
68 * until the value is positive and we write our incremented reader count.
69 */
70void __read_lock_failed(arch_rwlock_t *rw)
71{
72 u32 val;
73 int iterations = 0;
74 do {
75 delay_backoff(iterations++);
76 val = __insn_fetchaddgez4(&rw->lock, 1);
77 } while (unlikely(arch_write_val_locked(val)));
78}
79EXPORT_SYMBOL(__read_lock_failed);
80
81/*
82 * If we failed because there were readers, clear the "writer" bit
83 * so we don't block additional readers. Otherwise, there was another
84 * writer anyway, so our "fetchor" made no difference. Then wait,
85 * issuing periodic fetchor instructions, till we get the lock.
86 */
87void __write_lock_failed(arch_rwlock_t *rw, u32 val)
88{
89 int iterations = 0;
90 do {
91 if (!arch_write_val_locked(val))
92 val = __insn_fetchand4(&rw->lock, ~__WRITE_LOCK_BIT);
93 delay_backoff(iterations++);
94 val = __insn_fetchor4(&rw->lock, __WRITE_LOCK_BIT);
95 } while (val != 0);
96}
97EXPORT_SYMBOL(__write_lock_failed);