linux-kernel - [PATCH v2] lib/smp_processor_id: Use is_percpu

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Date:   Mon, 10 May 2021 21:43:58 +0800
From:   Yejune Deng <yejune.deng@...il.com>
To:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, tglx@...utronix.de, valentin.schneider@....com
Cc:     linux-kernel@...r.kernel.org, Yejune Deng <yejunedeng@...il.com>
Subject: [PATCH v2] lib/smp_processor_id: Use is_percpu_thread() check affinity

Use is_percpu_thread() instead of 'current->nr_cpus_allowed == 1',
and add PF_NO_SETAFFINITY flag in init_idle().This would be nice to
the sched_setaffinity(), and it also more readable.

v1->v2:
  - add PF_NO_SETAFFINITY flag in init_idle().

Signed-off-by: Yejune Deng <yejunedeng@...il.com>
---
 kernel/sched/core.c    | 2 +-
 lib/smp_processor_id.c | 6 +-----
 2 files changed, 2 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9143163..82e21ea 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7446,7 +7446,7 @@ void init_idle(struct task_struct *idle, int cpu)
 
 	idle->state = TASK_RUNNING;
 	idle->se.exec_start = sched_clock();
-	idle->flags |= PF_IDLE;
+	idle->flags |= PF_IDLE | PF_NO_SETAFFINITY;
 
 	scs_task_reset(idle);
 	kasan_unpoison_task_stack(idle);
diff --git a/lib/smp_processor_id.c b/lib/smp_processor_id.c
index 1c1dbd3..046ac62 100644
--- a/lib/smp_processor_id.c
+++ b/lib/smp_processor_id.c
@@ -19,11 +19,7 @@ unsigned int check_preemption_disabled(const char *what1, const char *what2)
 	if (irqs_disabled())
 		goto out;
 
-	/*
-	 * Kernel threads bound to a single CPU can safely use
-	 * smp_processor_id():
-	 */
-	if (current->nr_cpus_allowed == 1)
+	if (is_percpu_thread())
 		goto out;
 
 #ifdef CONFIG_SMP
-- 
2.7.4