x86, bts: remove recursion from get_context

Impact: cleanup

Optimistically allocate a DS context. It is extremely unlikely that
one already existed. This simplifies the code a lot.
Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/ds.c

@@ -232,53 +232,45 @@ static DEFINE_PER_CPU(struct ds_context *, system_context_array);
 
 #define system_context per_cpu(system_context_array, smp_processor_id())
 
-static struct ds_context *ds_get_context(struct task_struct *task)
+
+static inline struct ds_context *ds_get_context(struct task_struct *task)
 {
 	struct ds_context **p_context =
 		(task ? &task->thread.ds_ctx : &system_context);
-	struct ds_context *context = *p_context;
+	struct ds_context *context = NULL;
+	struct ds_context *new_context = NULL;
 	unsigned long irq;
 
-	if (!context) {
-		context = kzalloc(sizeof(*context), GFP_KERNEL);
-		if (!context)
+	/* Chances are small that we already have a context. */
+	new_context = kzalloc(sizeof(*new_context), GFP_KERNEL);
+	if (!new_context)
 		return NULL;
 
 	spin_lock_irqsave(&ds_lock, irq);
 
-		if (*p_context) {
-			kfree(context);
-
 	context = *p_context;
-		} else {
-			*p_context = context;
+	if (!context) {
+		context = new_context;
 
 		context->this = p_context;
 		context->task = task;
+		context->count = 0;
 
 		if (task)
 			set_tsk_thread_flag(task, TIF_DS_AREA_MSR);
 
 		if (!task || (task == current))
-				wrmsrl(MSR_IA32_DS_AREA,
-				       (unsigned long)context->ds);
-		}
-
-		context->count++;
+			wrmsrl(MSR_IA32_DS_AREA, (unsigned long)context->ds);
 
-		spin_unlock_irqrestore(&ds_lock, irq);
-	} else {
-		spin_lock_irqsave(&ds_lock, irq);
+		*p_context = context;
+	}
 
-		context = *p_context;
-		if (context)
 	context->count++;
 
 	spin_unlock_irqrestore(&ds_lock, irq);
 
-		if (!context)
-			context = ds_get_context(task);
-	}
+	if (context != new_context)
+		kfree(new_context);
 
 	return context;
 }