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From:   Reinette Chatre <reinette.chatre@intel.com>
To:     tglx@linutronix.de, fenghua.yu@intel.com, bp@alien8.de,
        tony.luck@intel.com
Cc:     kuo-lang.tseng@intel.com, shakeelb@google.com,
        valentin.schneider@arm.com, mingo@redhat.com, babu.moger@amd.com,
        james.morse@arm.com, hpa@zytor.com, x86@kernel.org,
        linux-kernel@vger.kernel.org,
        Reinette Chatre <reinette.chatre@intel.com>,
        stable@vger.kernel.org
Subject: [PATCH 1/3] x86/resctrl: Move setting task's active CPU in a mask into helpers
Date:   Thu,  3 Dec 2020 15:25:48 -0800
Message-Id: <77973e75a10bf7ef9b33c664544667deee9e1a8e.1607036601.git.reinette.chatre@intel.com>
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From: Fenghua Yu <fenghua.yu@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.yu@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Cc: stable@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