/*
* 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_MUTEX_H
#define _ASM_MUTEX_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
