x86: Use correct byte-sized register constraint in __xchg_op()

x86-64 can access the low half of any register, but i386 can only do
it with a subset of registers.  'r' causes compilation failures on i386,
but 'q' expresses the constraint properly.

Signed-off-by: Jeremy Fitzhardinge <jeremy@goop.org>
Link: http://lkml.kernel.org/r/4F7A3315.501@goop.org
Reported-by: Leigh Scott <leigh123linux@googlemail.com>
Tested-by: Thomas Reitmayr <treitmayr@devbase.at>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: <stable@vger.kernel.org> v3.3

diff --git a/arch/x86/include/asm/cmpxchg.h b/arch/x86/include/asm/cmpxchg.h
index b3b7332629096849d11866c017c4444f8d156f9e..bc18d0ed459a568a377ba74d924c42d84727511a 100644 (file)
--- a/arch/x86/include/asm/cmpxchg.h
+++ b/arch/x86/include/asm/cmpxchg.h
@@ -43,7 +43,7 @@ extern void __add_wrong_size(void)
                switch (sizeof(*(ptr))) {                               \
                case __X86_CASE_B:                                      \
                        asm volatile (lock #op "b %b0, %1\n"            \
-                                     : "+r" (__ret), "+m" (*(ptr))     \
+                                     : "+q" (__ret), "+m" (*(ptr))     \
                                      : : "memory", "cc");              \
                        break;                                          \
                case __X86_CASE_W:                                      \