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Ingo Molnarb8aa0362006-01-09 15:59:18 -08001/*
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(fastcall void (*)(atomic_t *), fail_fn); \
25 \
26 __asm__ __volatile__( \
27 LOCK " decl (%%rdi) \n" \
28 " js 2f \n" \
29 "1: \n" \
30 \
31 LOCK_SECTION_START("") \
32 "2: call "#fail_fn" \n" \
33 " jmp 1b \n" \
34 LOCK_SECTION_END \
35 \
36 :"=D" (dummy) \
37 : "D" (v) \
38 : "rax", "rsi", "rdx", "rcx", \
39 "r8", "r9", "r10", "r11", "memory"); \
40} while (0)
41
42/**
43 * __mutex_fastpath_lock_retval - try to take the lock by moving the count
44 * from 1 to a 0 value
45 * @count: pointer of type atomic_t
46 * @fail_fn: function to call if the original value was not 1
47 *
48 * Change the count from 1 to a value lower than 1, and call <fail_fn> if
49 * it wasn't 1 originally. This function returns 0 if the fastpath succeeds,
50 * or anything the slow path function returns
51 */
52static inline int
53__mutex_fastpath_lock_retval(atomic_t *count,
54 int fastcall (*fail_fn)(atomic_t *))
55{
56 if (unlikely(atomic_dec_return(count) < 0))
57 return fail_fn(count);
58 else
59 return 0;
60}
61
62/**
63 * __mutex_fastpath_unlock - increment and call function if nonpositive
64 * @v: pointer of type atomic_t
65 * @fail_fn: function to call if the result is nonpositive
66 *
67 * Atomically increments @v and calls <fail_fn> if the result is nonpositive.
68 */
69#define __mutex_fastpath_unlock(v, fail_fn) \
70do { \
71 unsigned long dummy; \
72 \
73 typecheck(atomic_t *, v); \
74 typecheck_fn(fastcall void (*)(atomic_t *), fail_fn); \
75 \
76 __asm__ __volatile__( \
77 LOCK " incl (%%rdi) \n" \
78 " jle 2f \n" \
79 "1: \n" \
80 \
81 LOCK_SECTION_START("") \
82 "2: call "#fail_fn" \n" \
83 " jmp 1b \n" \
84 LOCK_SECTION_END \
85 \
86 :"=D" (dummy) \
87 : "D" (v) \
88 : "rax", "rsi", "rdx", "rcx", \
89 "r8", "r9", "r10", "r11", "memory"); \
90} while (0)
91
92#define __mutex_slowpath_needs_to_unlock() 1
93
94/**
95 * __mutex_fastpath_trylock - try to acquire the mutex, without waiting
96 *
97 * @count: pointer of type atomic_t
98 * @fail_fn: fallback function
99 *
100 * Change the count from 1 to 0 and return 1 (success), or return 0 (failure)
101 * if it wasn't 1 originally. [the fallback function is never used on
102 * x86_64, because all x86_64 CPUs have a CMPXCHG instruction.]
103 */
104static inline int
105__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
106{
Linus Torvalds4cec8732006-01-11 15:50:47 -0800107 if (likely(atomic_cmpxchg(count, 1, 0) == 1))
Ingo Molnarb8aa0362006-01-09 15:59:18 -0800108 return 1;
109 else
110 return 0;
111}
112
113#endif