From: Ingo Molnar <mingo@elte.hu>
Date: Tue, 10 Jan 2006 21:07:44 +0000 (+0100)
Subject: [PATCH] fix i386 mutex fastpath on FRAME_POINTER && !DEBUG_MUTEXES
X-Git-Tag: v2.6.16-rc1~448
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=73165b88ffd29813bf73b331eaf90d3521443236;p=linux-2.6

[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: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---

diff --git a/include/asm-i386/mutex.h b/include/asm-i386/mutex.h
index 4e5e3de1b9..c657d4b09f 100644
--- a/include/asm-i386/mutex.h
+++ b/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)						\
diff --git a/kernel/mutex.c b/kernel/mutex.c
index 7eb9606614..d3dcb8b44b 100644
--- a/kernel/mutex.c
+++ b/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);
 }