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1/*
2 * Assembly implementation of the mutex fastpath, based on atomic
3 * decrement/increment.
4 *
5 * started by Ingo Molnar:
6 *
7 * Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
8 */
9#ifndef _ASM_MUTEX_H
10#define _ASM_MUTEX_H
11
12/**
13 * __mutex_fastpath_lock - decrement and call function if negative
14 * @v: pointer of type atomic_t
15 * @fail_fn: function to call if the result is negative
16 *
17 * Atomically decrements @v and calls <fail_fn> if the result is negative.
18 */
19#define __mutex_fastpath_lock(v, fail_fn) \
20do { \
21 unsigned long dummy; \
22 \
23 typecheck(atomic_t *, v); \
24 typecheck_fn(void (*)(atomic_t *), fail_fn); \
25 \
26 __asm__ __volatile__( \
27 LOCK_PREFIX " decl (%%rdi) \n" \
28 " jns 1f \n" \
29 " call "#fail_fn" \n" \
30 "1:" \
31 \
32 :"=D" (dummy) \
33 : "D" (v) \
34 : "rax", "rsi", "rdx", "rcx", \
35 "r8", "r9", "r10", "r11", "memory"); \
36} while (0)
37
38/**
39 * __mutex_fastpath_lock_retval - try to take the lock by moving the count
40 * from 1 to a 0 value
41 * @count: pointer of type atomic_t
42 * @fail_fn: function to call if the original value was not 1
43 *
44 * Change the count from 1 to a value lower than 1, and call <fail_fn> if
45 * it wasn't 1 originally. This function returns 0 if the fastpath succeeds,
46 * or anything the slow path function returns
47 */
48static inline int
49__mutex_fastpath_lock_retval(atomic_t *count,
50 int (*fail_fn)(atomic_t *))
51{
52 if (unlikely(atomic_dec_return(count) < 0))
53 return fail_fn(count);
54 else
55 return 0;
56}
57
58/**
59 * __mutex_fastpath_unlock - increment and call function if nonpositive
60 * @v: pointer of type atomic_t
61 * @fail_fn: function to call if the result is nonpositive
62 *
63 * Atomically increments @v and calls <fail_fn> if the result is nonpositive.
64 */
65#define __mutex_fastpath_unlock(v, fail_fn) \
66do { \
67 unsigned long dummy; \
68 \
69 typecheck(atomic_t *, v); \
70 typecheck_fn(void (*)(atomic_t *), fail_fn); \
71 \
72 __asm__ __volatile__( \
73 LOCK_PREFIX " incl (%%rdi) \n" \
74 " jg 1f \n" \
75 " call "#fail_fn" \n" \
76 "1: " \
77 \
78 :"=D" (dummy) \
79 : "D" (v) \
80 : "rax", "rsi", "rdx", "rcx", \
81 "r8", "r9", "r10", "r11", "memory"); \
82} while (0)
83
84#define __mutex_slowpath_needs_to_unlock() 1
85
86/**
87 * __mutex_fastpath_trylock - try to acquire the mutex, without waiting
88 *
89 * @count: pointer of type atomic_t
90 * @fail_fn: fallback function
91 *
92 * Change the count from 1 to 0 and return 1 (success), or return 0 (failure)
93 * if it wasn't 1 originally. [the fallback function is never used on
94 * x86_64, because all x86_64 CPUs have a CMPXCHG instruction.]
95 */
96static inline int
97__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
98{
99 if (likely(atomic_cmpxchg(count, 1, 0) == 1))
100 return 1;
101 else
102 return 0;
103}
104
105#endif