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_X86_MUTEX_64_H
10 #define _ASM_X86_MUTEX_64_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) \
20 do { \
21 unsigned long dummy; \
22 \
23 typecheck(atomic_t *, v); \
24 typecheck_fn(void (*)(atomic_t *), fail_fn); \
25 \
26 asm volatile(LOCK_PREFIX " decl (%%rdi)\n" \
27 " jns 1f \n" \
28 " call " #fail_fn "\n" \
29 "1:" \
30 : "=D" (dummy) \
31 : "D" (v) \
32 : "rax", "rsi", "rdx", "rcx", \
33 "r8", "r9", "r10", "r11", "memory"); \
34 } while (0)
35
36 /**
37 * __mutex_fastpath_lock_retval - try to take the lock by moving the count
38 * from 1 to a 0 value
39 * @count: pointer of type atomic_t
40 * @fail_fn: function to call if the original value was not 1
41 *
42 * Change the count from 1 to a value lower than 1, and call <fail_fn> if
43 * it wasn't 1 originally. This function returns 0 if the fastpath succeeds,
44 * or anything the slow path function returns
45 */
__mutex_fastpath_lock_retval(atomic_t * count,int (* fail_fn)(atomic_t *))46 static inline int __mutex_fastpath_lock_retval(atomic_t *count,
47 int (*fail_fn)(atomic_t *))
48 {
49 if (unlikely(atomic_dec_return(count) < 0))
50 return fail_fn(count);
51 else
52 return 0;
53 }
54
55 /**
56 * __mutex_fastpath_unlock - increment and call function if nonpositive
57 * @v: pointer of type atomic_t
58 * @fail_fn: function to call if the result is nonpositive
59 *
60 * Atomically increments @v and calls <fail_fn> if the result is nonpositive.
61 */
62 #define __mutex_fastpath_unlock(v, fail_fn) \
63 do { \
64 unsigned long dummy; \
65 \
66 typecheck(atomic_t *, v); \
67 typecheck_fn(void (*)(atomic_t *), fail_fn); \
68 \
69 asm volatile(LOCK_PREFIX " incl (%%rdi)\n" \
70 " jg 1f\n" \
71 " call " #fail_fn "\n" \
72 "1:" \
73 : "=D" (dummy) \
74 : "D" (v) \
75 : "rax", "rsi", "rdx", "rcx", \
76 "r8", "r9", "r10", "r11", "memory"); \
77 } while (0)
78
79 #define __mutex_slowpath_needs_to_unlock() 1
80
81 /**
82 * __mutex_fastpath_trylock - try to acquire the mutex, without waiting
83 *
84 * @count: pointer of type atomic_t
85 * @fail_fn: fallback function
86 *
87 * Change the count from 1 to 0 and return 1 (success), or return 0 (failure)
88 * if it wasn't 1 originally. [the fallback function is never used on
89 * x86_64, because all x86_64 CPUs have a CMPXCHG instruction.]
90 */
__mutex_fastpath_trylock(atomic_t * count,int (* fail_fn)(atomic_t *))91 static inline int __mutex_fastpath_trylock(atomic_t *count,
92 int (*fail_fn)(atomic_t *))
93 {
94 if (likely(atomic_cmpxchg(count, 1, 0) == 1))
95 return 1;
96 else
97 return 0;
98 }
99
100 #endif /* _ASM_X86_MUTEX_64_H */
101