[PATCH] fix i386 mutex fastpath on FRAME_POINTER && !DEBUG_MUTEXES

Call the mutex slowpath more conservatively - e.g.  FRAME_POINTERS can
change the calling convention, in which case a direct branch to the
slowpath becomes illegal.  Bug found by Hugh Dickins.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

include/asm-i386/mutex.h

@@ -28,7 +28,13 @@ do {									\
 									\
 	__asm__ __volatile__(						\
 		LOCK	"   decl (%%eax)	\n"			\
-			"   js "#fail_fn"	\n"			\
+			"   js 2f		\n"			\
+			"1:			\n"			\
+									\
+		LOCK_SECTION_START("")					\
+			"2: call "#fail_fn"	\n"			\
+			"   jmp 1b		\n"			\
+		LOCK_SECTION_END					\
 									\
 		:"=a" (dummy)						\
 		: "a" (count)						\
@@ -78,7 +84,13 @@ do {									\
 									\
 	__asm__ __volatile__(						\
 		LOCK	"   incl (%%eax)	\n"			\
-			"   jle "#fail_fn"	\n"			\
+			"   jle 2f		\n"			\
+			"1:			\n"			\
+									\
+		LOCK_SECTION_START("")					\
+			"2: call "#fail_fn"	\n"			\
+			"   jmp 1b		\n"			\
+		LOCK_SECTION_END					\
 									\
 		:"=a" (dummy)						\
 		: "a" (count)						\

kernel/mutex.c

@@ -84,12 +84,6 @@ void fastcall __sched mutex_lock(struct mutex *lock)
 	/*
 	 * The locking fastpath is the 1->0 transition from
 	 * 'unlocked' into 'locked' state.
-	 *
-	 * NOTE: if asm/mutex.h is included, then some architectures
-	 * rely on mutex_lock() having _no other code_ here but this
-	 * fastpath. That allows the assembly fastpath to do
-	 * tail-merging optimizations. (If you want to put testcode
-	 * here, do it under #ifndef CONFIG_MUTEX_DEBUG.)
 	 */
 	__mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath);
 }
@@ -115,8 +109,6 @@ void fastcall __sched mutex_unlock(struct mutex *lock)
 	/*
 	 * The unlocking fastpath is the 0->1 transition from 'locked'
 	 * into 'unlocked' state:
-	 *
-	 * NOTE: no other code must be here - see mutex_lock() .
 	 */
 	__mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath);
 }
@@ -261,7 +253,6 @@ __mutex_lock_interruptible_slowpath(atomic_t *lock_count __IP_DECL__);
  */
 int fastcall __sched mutex_lock_interruptible(struct mutex *lock)
 {
-	/* NOTE: no other code must be here - see mutex_lock() */
 	return __mutex_fastpath_lock_retval
 			(&lock->count, __mutex_lock_interruptible_slowpath);
 }