root/include/asm-x86/mutex_64.h

INCLUDED FROM

DEFINITIONS

1. __mutex_fastpath_lock_retval
2. __mutex_fastpath_trylock

/*
 * Assembly implementation of the mutex fastpath, based on atomic
 * decrement/increment.
 *
 * started by Ingo Molnar:
 *
 *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
 */
#ifndef ASM_X86__MUTEX_64_H
#define ASM_X86__MUTEX_64_H

/**
 * __mutex_fastpath_lock - decrement and call function if negative
 * @v: pointer of type atomic_t
 * @fail_fn: function to call if the result is negative
 *
 * Atomically decrements @v and calls <fail_fn> if the result is negative.
 */
#define __mutex_fastpath_lock(v, fail_fn)                       \
do {                                                            \
        unsigned long dummy;                                    \
                                                                \
        typecheck(atomic_t *, v);                               \
        typecheck_fn(void (*)(atomic_t *), fail_fn);            \
                                                                \
        asm volatile(LOCK_PREFIX "   decl (%%rdi)\n"            \
                     "   jns 1f         \n"                     \
                     "   call " #fail_fn "\n"                   \
                     "1:"                                       \
                     : "=D" (dummy)                             \
                     : "D" (v)                                  \
                     : "rax", "rsi", "rdx", "rcx",              \
                       "r8", "r9", "r10", "r11", "memory");     \
} while (0)

/**
 *  __mutex_fastpath_lock_retval - try to take the lock by moving the count
 *                                 from 1 to a 0 value
 *  @count: pointer of type atomic_t
 *  @fail_fn: function to call if the original value was not 1
 *
 * Change the count from 1 to a value lower than 1, and call <fail_fn> if
 * it wasn't 1 originally. This function returns 0 if the fastpath succeeds,
 * or anything the slow path function returns
 */
static inline int __mutex_fastpath_lock_retval(atomic_t *count,
                                               int (*fail_fn)(atomic_t *))
{
        if (unlikely(atomic_dec_return(count) < 0))
                return fail_fn(count);
        else
                return 0;
}

/**
 * __mutex_fastpath_unlock - increment and call function if nonpositive
 * @v: pointer of type atomic_t
 * @fail_fn: function to call if the result is nonpositive
 *
 * Atomically increments @v and calls <fail_fn> if the result is nonpositive.
 */
#define __mutex_fastpath_unlock(v, fail_fn)                     \
do {                                                            \
        unsigned long dummy;                                    \
                                                                \
        typecheck(atomic_t *, v);                               \
        typecheck_fn(void (*)(atomic_t *), fail_fn);            \
                                                                \
        asm volatile(LOCK_PREFIX "   incl (%%rdi)\n"            \
                     "   jg 1f\n"                               \
                     "   call " #fail_fn "\n"                   \
                     "1:"                                       \
                     : "=D" (dummy)                             \
                     : "D" (v)                                  \
                     : "rax", "rsi", "rdx", "rcx",              \
                       "r8", "r9", "r10", "r11", "memory");     \
} while (0)

#define __mutex_slowpath_needs_to_unlock()      1

/**
 * __mutex_fastpath_trylock - try to acquire the mutex, without waiting
 *
 *  @count: pointer of type atomic_t
 *  @fail_fn: fallback function
 *
 * Change the count from 1 to 0 and return 1 (success), or return 0 (failure)
 * if it wasn't 1 originally. [the fallback function is never used on
 * x86_64, because all x86_64 CPUs have a CMPXCHG instruction.]
 */
static inline int __mutex_fastpath_trylock(atomic_t *count,
                                           int (*fail_fn)(atomic_t *))
{
        if (likely(atomic_cmpxchg(count, 1, 0) == 1))
                return 1;
        else
                return 0;
}

#endif /* ASM_X86__MUTEX_64_H */