[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>

2 files changed, 14 insertions, 11 deletions

diff --git a/include/asm-i386/mutex.h b/include/asm-i386/mutex.h
index 4e5e3de1b9a6..c657d4b09f0a 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 7eb960661441..d3dcb8b44bac 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);
 }