mutex: Back out architecture specific check for negative mutex count

Linus suggested that probably all the supported architectures can
allow a negative mutex count without incorrect behavior, so we can
then back out the architecture specific change and allow the
mutex count to go to any negative number. That should further
reduce contention for non-x86 architecture.

Suggested-by: Linus Torvalds <[email protected]>
Signed-off-by: Waiman Long <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Chandramouleeswaran Aswin <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Norton Scott J <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: David Howells <[email protected]>
Cc: Dave Jones <[email protected]>
Cc: Clark Williams <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

2 files changed, 2 insertions, 17 deletions

diff --git a/arch/x86/include/asm/mutex.h b/arch/x86/include/asm/mutex.h
index bc2a0b0dcea6..7d3a48275394 100644
--- a/arch/x86/include/asm/mutex.h
+++ b/arch/x86/include/asm/mutex.h
@@ -3,13 +3,3 @@
 #else
 # include <asm/mutex_64.h>
 #endif
-
-#ifndef	__ASM_MUTEX_H
-#define	__ASM_MUTEX_H
-/*
- * For the x86 architecture, it allows any negative number (besides -1) in
- * the mutex count to indicate that some other threads are waiting on the
- * mutex.
- */
-#define __ARCH_ALLOW_ANY_NEGATIVE_MUTEX_COUNT	1
-#endif
diff --git a/kernel/mutex.c b/kernel/mutex.c
index 1dbd4210baef..ad53a664f113 100644
--- a/kernel/mutex.c
+++ b/kernel/mutex.c
@@ -38,15 +38,10 @@
 #endif
 
 /*
- * A mutex count of -1 indicates that waiters are sleeping waiting for the
- * mutex. Some architectures can allow any negative number, not just -1, for
- * this purpose.
+ * A negative mutex count indicates that waiters are sleeping waiting for the
+ * mutex.
  */
-#ifdef __ARCH_ALLOW_ANY_NEGATIVE_MUTEX_COUNT
 #define	MUTEX_SHOW_NO_WAITER(mutex)	(atomic_read(&(mutex)->count) >= 0)
-#else
-#define	MUTEX_SHOW_NO_WAITER(mutex)	(atomic_read(&(mutex)->count) != -1)
-#endif
 
 void
 __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)