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-rw-r--r--include/asm-i386/mutex.h136
1 files changed, 136 insertions, 0 deletions
diff --git a/include/asm-i386/mutex.h b/include/asm-i386/mutex.h
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+/*
+ * 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 - try to take the lock by moving the count
+ * from 1 to a 0 value
+ * @count: pointer of type atomic_t
+ * @fn: function to call if the original value was not 1
+ *
+ * Change the count from 1 to a value lower than 1, and call <fn> if it
+ * wasn't 1 originally. This function MUST leave the value lower than 1
+ * even when the "1" assertion wasn't true.
+ */
+#define __mutex_fastpath_lock(count, fail_fn) \
+do { \
+ unsigned int dummy; \
+ \
+ typecheck(atomic_t *, count); \
+ typecheck_fn(fastcall void (*)(atomic_t *), fail_fn); \
+ \
+ __asm__ __volatile__( \
+ LOCK " decl (%%eax) \n" \
+ " js 2f \n" \
+ "1: \n" \
+ \
+ LOCK_SECTION_START("") \
+ "2: call "#fail_fn" \n" \
+ " jmp 1b \n" \
+ LOCK_SECTION_END \
+ \
+ :"=a" (dummy) \
+ : "a" (count) \
+ : "memory", "ecx", "edx"); \
+} 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 fastcall (*fail_fn)(atomic_t *))
+{
+ if (unlikely(atomic_dec_return(count) < 0))
+ return fail_fn(count);
+ else
+ return 0;
+}
+
+/**
+ * __mutex_fastpath_unlock - try to promote the mutex from 0 to 1
+ * @count: pointer of type atomic_t
+ * @fail_fn: function to call if the original value was not 0
+ *
+ * try to promote the mutex from 0 to 1. if it wasn't 0, call <fail_fn>.
+ * In the failure case, this function is allowed to either set the value
+ * to 1, or to set it to a value lower than 1.
+ *
+ * If the implementation sets it to a value of lower than 1, the
+ * __mutex_slowpath_needs_to_unlock() macro needs to return 1, it needs
+ * to return 0 otherwise.
+ */
+#define __mutex_fastpath_unlock(count, fail_fn) \
+do { \
+ unsigned int dummy; \
+ \
+ typecheck(atomic_t *, count); \
+ typecheck_fn(fastcall void (*)(atomic_t *), fail_fn); \
+ \
+ __asm__ __volatile__( \
+ LOCK " incl (%%eax) \n" \
+ " jle 2f \n" \
+ "1: \n" \
+ \
+ LOCK_SECTION_START("") \
+ "2: call "#fail_fn" \n" \
+ " jmp 1b \n" \
+ LOCK_SECTION_END \
+ \
+ :"=a" (dummy) \
+ : "a" (count) \
+ : "memory", "ecx", "edx"); \
+} 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 a value lower than 1, and return 0 (failure)
+ * if it wasn't 1 originally, or return 1 (success) otherwise. This function
+ * MUST leave the value lower than 1 even when the "1" assertion wasn't true.
+ * Additionally, if the value was < 0 originally, this function must not leave
+ * it to 0 on failure.
+ */
+static inline int
+__mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
+{
+ /*
+ * We have two variants here. The cmpxchg based one is the best one
+ * because it never induce a false contention state. It is included
+ * here because architectures using the inc/dec algorithms over the
+ * xchg ones are much more likely to support cmpxchg natively.
+ *
+ * If not we fall back to the spinlock based variant - that is
+ * just as efficient (and simpler) as a 'destructive' probing of
+ * the mutex state would be.
+ */
+#ifdef __HAVE_ARCH_CMPXCHG
+ if (likely(atomic_cmpxchg(count, 1, 0) == 1))
+ return 1;
+ return 0;
+#else
+ return fail_fn(count);
+#endif
+}
+
+#endif