x86, ptrace: PEBS support, warning fix

arch/x86/kernel/process_32.c:566: warning: unused variable 'ds_next'
arch/x86/kernel/process_32.c:566: warning: unused variable 'ds_prev'

Cc: Markus Metzger <markus.t.metzger@intel.com>
Cc: Andi Kleen <ak@suse.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: "Siddha, Suresh B" <suresh.b.siddha@intel.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: Michael Kerrisk <mtk.manpages@googlemail.com>
Cc: <juan.villacis@intel.com>
Cc: stephane eranian <eranian@googlemail.com>
Cc: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/process_32.c

@@ -484,20 +484,13 @@ int set_tsc_mode(unsigned int val)
 	return 0;
 }
 
-static noinline void
-__switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
-		 struct tss_struct *tss)
+#ifdef CONFIG_X86_DS
+static int update_debugctl(struct thread_struct *prev,
+			struct thread_struct *next, unsigned long debugctl)
 {
-	struct thread_struct *prev, *next;
-	unsigned long debugctl;
-	unsigned long ds_prev = 0, ds_next = 0;
+	unsigned long ds_prev = 0;
+	unsigned long ds_next = 0;
 
-	prev = &prev_p->thread;
-	next = &next_p->thread;
-
-	debugctl = prev->debugctlmsr;
-
-#ifdef CONFIG_X86_DS
 	if (prev->ds_ctx)
 		ds_prev = (unsigned long)prev->ds_ctx->ds;
 	if (next->ds_ctx)
@@ -510,8 +503,28 @@ __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
 		update_debugctlmsr(0);
 		wrmsr(MSR_IA32_DS_AREA, ds_next, 0);
 	}
+	return debugctl;
+}
+#else
+static int update_debugctl(struct thread_struct *prev,
+			struct thread_struct *next, unsigned long debugctl)
+{
+	return debugctl;
+}
 #endif /* CONFIG_X86_DS */
 
+static noinline void
+__switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
+		 struct tss_struct *tss)
+{
+	struct thread_struct *prev, *next;
+	unsigned long debugctl;
+
+	prev = &prev_p->thread;
+	next = &next_p->thread;
+
+	debugctl = update_debugctl(prev, next, prev->debugctlmsr);
+
 	if (next->debugctlmsr != debugctl)
 		update_debugctlmsr(next->debugctlmsr);