x86: replace LOCK_PREFIX in futex.h

The exception fixup for the futex macros __futex_atomic_op1/2 and
futex_atomic_cmpxchg_inatomic() is missing an entry when the lock
prefix is replaced by a NOP via SMP alternatives.

Chuck Ebert tracked this down from the information provided in:
https://bugzilla.redhat.com/show_bug.cgi?id=429412

A possible solution would be to add another fixup after the
LOCK_PREFIX, so both the LOCK and NOP case have their own entry in the
exception table, but it's not really worth the trouble.

Simply replace LOCK_PREFIX with lock and keep those untouched by SMP
alternatives.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/include/asm-x86/futex.h b/include/asm-x86/futex.h
index 62828d6..9d91926 100644 (file)
--- a/include/asm-x86/futex.h
+++ b/include/asm-x86/futex.h
@@ -30,7 +30,7 @@
 "1:    movl    %2, %0\n                                        \
        movl    %0, %3\n"                                       \
        insn "\n"                                               \
-"2:    " LOCK_PREFIX "cmpxchgl %3, %2\n                        \
+"2:    lock; cmpxchgl %3, %2\n                                 \
        jnz     1b\n                                            \
 3:     .section .fixup,\"ax\"\n                                \
 4:     mov     %5, %1\n                                        \
@@ -72,7 +72,7 @@ futex_atomic_op_inuser(int encoded_op, int __user *uaddr)
                __futex_atomic_op1("xchgl %0, %2", ret, oldval, uaddr, oparg);
                break;
        case FUTEX_OP_ADD:
-               __futex_atomic_op1(LOCK_PREFIX "xaddl %0, %2", ret, oldval,
+               __futex_atomic_op1("lock; xaddl %0, %2", ret, oldval,
                                   uaddr, oparg);
                break;
        case FUTEX_OP_OR:
@@ -111,8 +111,8 @@ futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)
                return -EFAULT;
 
        __asm__ __volatile__(
-               "1:     " LOCK_PREFIX "cmpxchgl %3, %1          \n"
 
+               "1:     lock; cmpxchgl %3, %1                   \n"
                "2:     .section .fixup, \"ax\"                 \n"
                "3:     mov     %2, %0                          \n"
                "       jmp     2b                              \n"