linux-kernel - [patch 05/10] sched/core: Split __set_cpus_allowed

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Date:   Thu, 17 Sep 2020 11:42:07 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Sebastian Siewior <bigeasy@...utronix.de>,
        Qais Yousef <qais.yousef@....com>,
        Scott Wood <swood@...hat.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Vincent Donnefort <vincent.donnefort@....com>
Subject: [patch 05/10] sched/core: Split __set_cpus_allowed_ptr()

Split the function so the actual work part can be reused and called from
places which hold rq::lock already.

No functional change.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 kernel/sched/core.c |   64 ++++++++++++++++++++++++++++++----------------------
 1 file changed, 38 insertions(+), 26 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1863,34 +1863,17 @@ void do_set_cpus_allowed(struct task_str
 		set_next_task(rq, p);
 }
 
-/*
- * Change a given task's CPU affinity. Migrate the thread to a
- * proper CPU and schedule it away if the CPU it's executing on
- * is removed from the allowed bitmask.
- *
- * NOTE: the caller must have a valid reference to the task, the
- * task must not exit() & deallocate itself prematurely. The
- * call is not atomic; no spinlocks may be held.
- */
-static int __set_cpus_allowed_ptr(struct task_struct *p,
-				  const struct cpumask *new_mask, bool check)
+static int set_cpus_allowed_ptr_locked(struct task_struct *p,
+				       const struct cpumask *new_mask,
+				       bool check,
+				       struct rq *rq, struct rq_flags *rf)
 {
 	const struct cpumask *cpu_valid_mask = cpu_active_mask;
 	unsigned int dest_cpu;
-	struct rq_flags rf;
-	struct rq *rq;
 	int ret = 0;
 
-	rq = task_rq_lock(p, &rf);
 	update_rq_clock(rq);
 
-	if (p->flags & PF_KTHREAD) {
-		/*
-		 * Kernel threads are allowed on online && !active CPUs
-		 */
-		cpu_valid_mask = cpu_online_mask;
-	}
-
 	/*
 	 * Must re-check here, to close a race against __kthread_bind(),
 	 * sched_setaffinity() is not guaranteed to observe the flag.
@@ -1900,8 +1883,12 @@ static int __set_cpus_allowed_ptr(struct
 		goto out;
 	}
 
-	if (cpumask_equal(&p->cpus_mask, new_mask))
-		goto out;
+	if (p->flags & PF_KTHREAD) {
+		/*
+		 * Kernel threads are allowed on online && !active CPUs
+		 */
+		cpu_valid_mask = cpu_online_mask;
+	}
 
 	/*
 	 * Picking a ~random cpu helps in cases where we are changing affinity
@@ -1933,7 +1920,7 @@ static int __set_cpus_allowed_ptr(struct
 	if (task_running(rq, p) || p->state == TASK_WAKING) {
 		struct migration_arg arg = { p, dest_cpu };
 		/* Need help from migration thread: drop lock and wait. */
-		task_rq_unlock(rq, p, &rf);
+		task_rq_unlock(rq, p, rf);
 		stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg);
 		return 0;
 	} else if (task_on_rq_queued(p)) {
@@ -1941,10 +1928,35 @@ static int __set_cpus_allowed_ptr(struct
 		 * OK, since we're going to drop the lock immediately
 		 * afterwards anyway.
 		 */
-		rq = move_queued_task(rq, &rf, p, dest_cpu);
+		rq = move_queued_task(rq, rf, p, dest_cpu);
 	}
 out:
-	task_rq_unlock(rq, p, &rf);
+	task_rq_unlock(rq, p, rf);
+	return ret;
+}
+
+/*
+ * Change a given task's CPU affinity. Migrate the thread to a
+ * proper CPU and schedule it away if the CPU it's executing on
+ * is removed from the allowed bitmask.
+ *
+ * NOTE: the caller must have a valid reference to the task, the
+ * task must not exit() & deallocate itself prematurely. The
+ * call is not atomic; no spinlocks may be held.
+ */
+static int __set_cpus_allowed_ptr(struct task_struct *p,
+				  const struct cpumask *new_mask, bool check)
+{
+	struct rq_flags rf;
+	struct rq *rq;
+	int ret = 0;
+
+	rq = task_rq_lock(p, &rf);
+
+	if (cpumask_equal(&p->cpus_mask, new_mask))
+		task_rq_unlock(rq, p, &rf);
+	else
+		ret = set_cpus_allowed_ptr_locked(p, new_mask, check, rq, &rf);
 
 	return ret;
 }