2 * Assembly implementation of the mutex fastpath, based on atomic
5 * started by Ingo Molnar:
7 * Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
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
17 * Atomically decrements @v and calls <fail_fn> if the result is negative.
19 #define __mutex_fastpath_lock(v, fail_fn) \
21 unsigned long dummy; \
23 typecheck(atomic_t *, v); \
24 typecheck_fn(void (*)(atomic_t *), fail_fn); \
26 asm volatile(LOCK_PREFIX " decl (%%rdi)\n" \
28 " call " #fail_fn "\n" \
32 : "rax", "rsi", "rdx", "rcx", \
33 "r8", "r9", "r10", "r11", "memory"); \
37 * __mutex_fastpath_lock_retval - try to take the lock by moving the count
39 * @count: pointer of type atomic_t
40 * @fail_fn: function to call if the original value was not 1
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
46 static inline int __mutex_fastpath_lock_retval(atomic_t *count,
47 int (*fail_fn)(atomic_t *))
49 if (unlikely(atomic_dec_return(count) < 0))
50 return fail_fn(count);
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
60 * Atomically increments @v and calls <fail_fn> if the result is nonpositive.
62 #define __mutex_fastpath_unlock(v, fail_fn) \
64 unsigned long dummy; \
66 typecheck(atomic_t *, v); \
67 typecheck_fn(void (*)(atomic_t *), fail_fn); \
69 asm volatile(LOCK_PREFIX " incl (%%rdi)\n" \
71 " call " #fail_fn "\n" \
75 : "rax", "rsi", "rdx", "rcx", \
76 "r8", "r9", "r10", "r11", "memory"); \
79 #define __mutex_slowpath_needs_to_unlock() 1
82 * __mutex_fastpath_trylock - try to acquire the mutex, without waiting
84 * @count: pointer of type atomic_t
85 * @fail_fn: fallback function
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.]
91 static inline int __mutex_fastpath_trylock(atomic_t *count,
92 int (*fail_fn)(atomic_t *))
94 if (likely(atomic_cmpxchg(count, 1, 0) == 1))