114 lines
3.1 KiB
C
114 lines
3.1 KiB
C
/*
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* Assembly implementation of the mutex fastpath, based on atomic
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* decrement/increment.
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*
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* started by Ingo Molnar:
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*
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* Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
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*/
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#ifndef _ASM_MUTEX_H
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#define _ASM_MUTEX_H
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/**
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* __mutex_fastpath_lock - decrement and call function if negative
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* @v: pointer of type atomic_t
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* @fail_fn: function to call if the result is negative
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*
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* Atomically decrements @v and calls <fail_fn> if the result is negative.
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*/
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#define __mutex_fastpath_lock(v, fail_fn) \
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do { \
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unsigned long dummy; \
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\
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typecheck(atomic_t *, v); \
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typecheck_fn(fastcall void (*)(atomic_t *), fail_fn); \
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\
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__asm__ __volatile__( \
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LOCK_PREFIX " decl (%%rdi) \n" \
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" js 2f \n" \
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"1: \n" \
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\
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LOCK_SECTION_START("") \
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"2: call "#fail_fn" \n" \
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" jmp 1b \n" \
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LOCK_SECTION_END \
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\
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:"=D" (dummy) \
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: "D" (v) \
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: "rax", "rsi", "rdx", "rcx", \
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"r8", "r9", "r10", "r11", "memory"); \
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} while (0)
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/**
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* __mutex_fastpath_lock_retval - try to take the lock by moving the count
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* from 1 to a 0 value
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* @count: pointer of type atomic_t
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* @fail_fn: function to call if the original value was not 1
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*
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* Change the count from 1 to a value lower than 1, and call <fail_fn> if
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* it wasn't 1 originally. This function returns 0 if the fastpath succeeds,
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* or anything the slow path function returns
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*/
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static inline int
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__mutex_fastpath_lock_retval(atomic_t *count,
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int fastcall (*fail_fn)(atomic_t *))
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{
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if (unlikely(atomic_dec_return(count) < 0))
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return fail_fn(count);
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else
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return 0;
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}
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/**
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* __mutex_fastpath_unlock - increment and call function if nonpositive
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* @v: pointer of type atomic_t
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* @fail_fn: function to call if the result is nonpositive
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*
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* Atomically increments @v and calls <fail_fn> if the result is nonpositive.
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*/
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#define __mutex_fastpath_unlock(v, fail_fn) \
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do { \
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unsigned long dummy; \
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\
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typecheck(atomic_t *, v); \
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typecheck_fn(fastcall void (*)(atomic_t *), fail_fn); \
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\
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__asm__ __volatile__( \
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LOCK_PREFIX " incl (%%rdi) \n" \
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" jle 2f \n" \
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"1: \n" \
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\
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LOCK_SECTION_START("") \
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"2: call "#fail_fn" \n" \
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" jmp 1b \n" \
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LOCK_SECTION_END \
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\
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:"=D" (dummy) \
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: "D" (v) \
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: "rax", "rsi", "rdx", "rcx", \
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"r8", "r9", "r10", "r11", "memory"); \
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} while (0)
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#define __mutex_slowpath_needs_to_unlock() 1
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/**
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* __mutex_fastpath_trylock - try to acquire the mutex, without waiting
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*
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* @count: pointer of type atomic_t
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* @fail_fn: fallback function
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*
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* Change the count from 1 to 0 and return 1 (success), or return 0 (failure)
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* if it wasn't 1 originally. [the fallback function is never used on
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* x86_64, because all x86_64 CPUs have a CMPXCHG instruction.]
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*/
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static inline int
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__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
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{
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if (likely(atomic_cmpxchg(count, 1, 0) == 1))
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return 1;
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else
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return 0;
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}
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#endif
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