a41b56efa7
This will allow me to call functions that have multiple arguments if fastpath fails. This is required to support ticket mutexes, because they need to be able to pass an extra argument to the fail function. Originally I duplicated the functions, by adding __mutex_fastpath_lock_retval_arg. This ended up being just a duplication of the existing function, so a way to test if fastpath was called ended up being better. This also cleaned up the reservation mutex patch some by being able to call an atomic_set instead of atomic_xchg, and making it easier to detect if the wrong unlock function was previously used. Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: dri-devel@lists.freedesktop.org Cc: linaro-mm-sig@lists.linaro.org Cc: robclark@gmail.com Cc: rostedt@goodmis.org Cc: daniel@ffwll.ch Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/20130620113105.4001.83929.stgit@patser Signed-off-by: Ingo Molnar <mingo@kernel.org>
123 lines
3.7 KiB
C
123 lines
3.7 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_X86_MUTEX_32_H
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#define _ASM_X86_MUTEX_32_H
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#include <asm/alternative.h>
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/**
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* __mutex_fastpath_lock - 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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* @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 <fn> if it
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* wasn't 1 originally. This function MUST leave the value lower than 1
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* even when the "1" assertion wasn't true.
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*/
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#define __mutex_fastpath_lock(count, fail_fn) \
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do { \
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unsigned int dummy; \
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\
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typecheck(atomic_t *, count); \
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typecheck_fn(void (*)(atomic_t *), fail_fn); \
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\
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asm volatile(LOCK_PREFIX " decl (%%eax)\n" \
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" jns 1f \n" \
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" call " #fail_fn "\n" \
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"1:\n" \
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: "=a" (dummy) \
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: "a" (count) \
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: "memory", "ecx", "edx"); \
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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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*
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* Change the count from 1 to a value lower than 1. This function returns 0
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* if the fastpath succeeds, or -1 otherwise.
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*/
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static inline int __mutex_fastpath_lock_retval(atomic_t *count)
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{
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if (unlikely(atomic_dec_return(count) < 0))
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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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/**
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* __mutex_fastpath_unlock - try to promote the mutex from 0 to 1
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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 0
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*
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* try to promote the mutex from 0 to 1. if it wasn't 0, call <fail_fn>.
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* In the failure case, this function is allowed to either set the value
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* to 1, or to set it to a value lower than 1.
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*
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* If the implementation sets it to a value of lower than 1, the
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* __mutex_slowpath_needs_to_unlock() macro needs to return 1, it needs
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* to return 0 otherwise.
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*/
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#define __mutex_fastpath_unlock(count, fail_fn) \
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do { \
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unsigned int dummy; \
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\
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typecheck(atomic_t *, count); \
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typecheck_fn(void (*)(atomic_t *), fail_fn); \
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\
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asm volatile(LOCK_PREFIX " incl (%%eax)\n" \
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" jg 1f\n" \
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" call " #fail_fn "\n" \
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"1:\n" \
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: "=a" (dummy) \
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: "a" (count) \
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: "memory", "ecx", "edx"); \
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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 a value lower than 1, and return 0 (failure)
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* if it wasn't 1 originally, or return 1 (success) otherwise. This function
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* MUST leave the value lower than 1 even when the "1" assertion wasn't true.
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* Additionally, if the value was < 0 originally, this function must not leave
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* it to 0 on failure.
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*/
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static inline int __mutex_fastpath_trylock(atomic_t *count,
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int (*fail_fn)(atomic_t *))
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{
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/*
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* We have two variants here. The cmpxchg based one is the best one
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* because it never induce a false contention state. It is included
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* here because architectures using the inc/dec algorithms over the
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* xchg ones are much more likely to support cmpxchg natively.
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*
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* If not we fall back to the spinlock based variant - that is
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* just as efficient (and simpler) as a 'destructive' probing of
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* the mutex state would be.
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*/
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#ifdef __HAVE_ARCH_CMPXCHG
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if (likely(atomic_cmpxchg(count, 1, 0) == 1))
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return 1;
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return 0;
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#else
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return fail_fn(count);
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#endif
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}
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#endif /* _ASM_X86_MUTEX_32_H */
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