x86, um: ... and asm-x86 move

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 125 insertions, 0 deletions

diff --git a/arch/x86/include/asm/mutex_32.h b/arch/x86/include/asm/mutex_32.h
new file mode 100644
index 000000000000..25c16d8ba3c7
--- /dev/null
+++ b/arch/x86/include/asm/mutex_32.h
@@ -0,0 +1,125 @@
+/*
+ * 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_32_H
+#define ASM_X86__MUTEX_32_H
+
+#include <asm/alternative.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(void (*)(atomic_t *), fail_fn);		\
+								\
+	asm volatile(LOCK_PREFIX "   decl (%%eax)\n"		\
+		     "   jns 1f	\n"				\
+		     "   call " #fail_fn "\n"			\
+		     "1:\n"					\
+		     : "=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 (*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(void (*)(atomic_t *), fail_fn);		\
+								\
+	asm volatile(LOCK_PREFIX "   incl (%%eax)\n"		\
+		     "   jg	1f\n"				\
+		     "   call " #fail_fn "\n"			\
+		     "1:\n"					\
+		     : "=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 /* ASM_X86__MUTEX_32_H */