percpu: Omit segment prefix in the UP case for cmpxchg_double

Omit the segment prefix in the UP case. GS is not used then
and we will generate segfaults if cmpxchg16b is used otherwise.

Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 4 deletions

diff --git a/arch/x86/lib/cmpxchg16b_emu.S b/arch/x86/lib/cmpxchg16b_emu.S
index 3e8b08a6de2..1e572c507d0 100644
--- a/arch/x86/lib/cmpxchg16b_emu.S
+++ b/arch/x86/lib/cmpxchg16b_emu.S
@@ -10,6 +10,12 @@
 #include <asm/frame.h>
 #include <asm/dwarf2.h>
 
+#ifdef CONFIG_SMP
+#define SEG_PREFIX %gs:
+#else
+#define SEG_PREFIX
+#endif
+
 .text
 
 /*
@@ -37,13 +43,13 @@ this_cpu_cmpxchg16b_emu:
         pushf
         cli
 
-        cmpq %gs:(%rsi), %rax
+        cmpq SEG_PREFIX(%rsi), %rax
         jne not_same
-        cmpq %gs:8(%rsi), %rdx
+        cmpq SEG_PREFIX 8(%rsi), %rdx
         jne not_same
 
-        movq %rbx, %gs:(%rsi)
-        movq %rcx, %gs:8(%rsi)
+        movq %rbx, SEG_PREFIX(%rsi)
+        movq %rcx, SEG_PREFIX 8(%rsi)
 
         popf
         mov $1, %al