x86: kernel_thread() -- initialize SS to a known state

Before the kernel_thread was converted into "C" we had
pt_regs::ss set to __KERNEL_DS (by SAVE_ALL asm macro).

Though I must admit I didn't find any *explicit* load of
%ss from this structure the better to be on a safe side
and set it to a known value.
Signed-off-by: NCyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: NIan Campbell <ian.campbell@citrix.com>
Cc: Christian Kujau <lists@nerdbynature.de>
Cc: Jeremy Fitzhardinge <Jeremy.Fitzhardinge@citrix.com>
Cc: Brian Gerst <brgerst@gmail.com>
LKML-Reference: <1263377768-19600-1-git-send-email-ian.campbell@citrix.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/kernel/process.c

@@ -288,6 +288,8 @@ int kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
 	regs.es = __USER_DS;
 	regs.fs = __KERNEL_PERCPU;
 	regs.gs = __KERNEL_STACK_CANARY;
+#else
+	regs.ss = __KERNEL_DS;
 #endif
 
 	regs.orig_ax = -1;