[PATCH 1/3] x86/resctrl: Move setting task's active CPU in a mask into helpers

[Reinette Chatre]

From: Fenghua Yu <fenghua...@intel.com>

The code of setting the CPU on which a task is running in a CPU mask is
moved into a couple of helpers. The new helper task_on_cpu() will be
reused shortly.

Signed-off-by: Fenghua Yu <fenghua...@intel.com>
Signed-off-by: Reinette Chatre <reinette.cha...@intel.com>
Reviewed-by: Tony Luck <tony.l...@intel.com>
Cc: sta...@vger.kernel.org
---
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 47 +++++++++++++++++++-------
 1 file changed, 34 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c 
b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 6f4ca4bea625..68db7d2dec8f 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -525,6 +525,38 @@ static void rdtgroup_remove(struct rdtgroup *rdtgrp)
        kfree(rdtgrp);
 }
 
+#ifdef CONFIG_SMP
+/* Get the CPU if the task is on it. */
+static bool task_on_cpu(struct task_struct *t, int *cpu)
+{
+       /*
+        * This is safe on x86 w/o barriers as the ordering of writing to
+        * task_cpu() and t->on_cpu is reverse to the reading here. The
+        * detection is inaccurate as tasks might move or schedule before
+        * the smp function call takes place. In such a case the function
+        * call is pointless, but there is no other side effect.
+        */
+       if (t->on_cpu) {
+               *cpu = task_cpu(t);
+
+               return true;
+       }
+
+       return false;
+}
+
+static void set_task_cpumask(struct task_struct *t, struct cpumask *mask)
+{
+       int cpu;
+
+       if (mask && task_on_cpu(t, &cpu))
+               cpumask_set_cpu(cpu, mask);
+}
+#else
+static inline void
+set_task_cpumask(struct task_struct *t, struct cpumask *mask) { }
+#endif
+
 struct task_move_callback {
        struct callback_head    work;
        struct rdtgroup         *rdtgrp;
@@ -2327,19 +2359,8 @@ static void rdt_move_group_tasks(struct rdtgroup *from, 
struct rdtgroup *to,
                        t->closid = to->closid;
                        t->rmid = to->mon.rmid;
 
-#ifdef CONFIG_SMP
-                       /*
-                        * This is safe on x86 w/o barriers as the ordering
-                        * of writing to task_cpu() and t->on_cpu is
-                        * reverse to the reading here. The detection is
-                        * inaccurate as tasks might move or schedule
-                        * before the smp function call takes place. In
-                        * such a case the function call is pointless, but
-                        * there is no other side effect.
-                        */
-                       if (mask && t->on_cpu)
-                               cpumask_set_cpu(task_cpu(t), mask);
-#endif
+                       /* If the task is on a CPU, set the CPU in the mask. */
+                       set_task_cpumask(t, mask);
                }
        }
        read_unlock(&tasklist_lock);
-- 
2.26.2