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>

diff --git a/arch/x86/kernel/ds.c b/arch/x86/kernel/ds.c
index dc1e712..0dc7959 100644 (file)
--- a/arch/x86/kernel/ds.c
+++ b/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)
-                       return NULL;
-
-               spin_lock_irqsave(&ds_lock, irq);
-
-               if (*p_context) {
-                       kfree(context);
+       /* Chances are small that we already have a context. */
+       new_context = kzalloc(sizeof(*new_context), GFP_KERNEL);
+       if (!new_context)
+               return NULL;
 
-                       context = *p_context;
-               } else {
-                       *p_context = context;
+       spin_lock_irqsave(&ds_lock, irq);
 
-                       context->this = p_context;
-                       context->task = task;
+       context = *p_context;
+       if (!context) {
+               context = new_context;
 
-                       if (task)
-                               set_tsk_thread_flag(task, TIF_DS_AREA_MSR);
+               context->this = p_context;
+               context->task = task;
+               context->count = 0;
 
-                       if (!task || (task == current))
-                               wrmsrl(MSR_IA32_DS_AREA,
-                                      (unsigned long)context->ds);
-               }
+               if (task)
+                       set_tsk_thread_flag(task, TIF_DS_AREA_MSR);
 
-               context->count++;
+               if (!task || (task == current))
+                       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++;
+       context->count++;
 
-               spin_unlock_irqrestore(&ds_lock, irq);
+       spin_unlock_irqrestore(&ds_lock, irq);
 
-               if (!context)
-                       context = ds_get_context(task);
-       }
+       if (context != new_context)
+               kfree(new_context);
 
        return context;
 }