linux-kernel - [PATCH RT 22/32] sched: migrate_enable: Use select_fallback

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Date:   Fri, 17 Jan 2020 12:41:33 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org,
        linux-rt-users <linux-rt-users@...r.kernel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Carsten Emde <C.Emde@...dl.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        John Kacur <jkacur@...hat.com>,
        Julia Cartwright <julia@...com>,
        Daniel Wagner <wagi@...om.org>,
        Tom Zanussi <zanussi@...nel.org>, Scott Wood <swood@...hat.com>
Subject: [PATCH RT 22/32] sched: migrate_enable: Use select_fallback_rq()

4.19.94-rt39-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Scott Wood <swood@...hat.com>

[ Upstream commit adfa969d4cfcc995a9d866020124e50f1827d2d1 ]

migrate_enable() currently open-codes a variant of select_fallback_rq().
However, it does not have the "No more Mr. Nice Guy" fallback and thus
it will pass an invalid CPU to the migration thread if cpus_mask only
contains a CPU that is !active.

Signed-off-by: Scott Wood <swood@...hat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 kernel/sched/core.c | 25 ++++++++++---------------
 1 file changed, 10 insertions(+), 15 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d9a3f88508ee..6fd3f7b4d7d8 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7335,6 +7335,7 @@ void migrate_enable(void)
 	if (p->migrate_disable_update) {
 		struct rq *rq;
 		struct rq_flags rf;
+		int cpu = task_cpu(p);
 
 		rq = task_rq_lock(p, &rf);
 		update_rq_clock(rq);
@@ -7344,21 +7345,15 @@ void migrate_enable(void)
 
 		p->migrate_disable_update = 0;
 
-		WARN_ON(smp_processor_id() != task_cpu(p));
-		if (!cpumask_test_cpu(task_cpu(p), &p->cpus_mask)) {
-			const struct cpumask *cpu_valid_mask = cpu_active_mask;
-			struct migration_arg arg;
-			unsigned int dest_cpu;
-
-			if (p->flags & PF_KTHREAD) {
-				/*
-				 * Kernel threads are allowed on online && !active CPUs
-				 */
-				cpu_valid_mask = cpu_online_mask;
-			}
-			dest_cpu = cpumask_any_and(cpu_valid_mask, &p->cpus_mask);
-			arg.task = p;
-			arg.dest_cpu = dest_cpu;
+		WARN_ON(smp_processor_id() != cpu);
+		if (!cpumask_test_cpu(cpu, &p->cpus_mask)) {
+			struct migration_arg arg = { p };
+			struct rq_flags rf;
+
+			rq = task_rq_lock(p, &rf);
+			update_rq_clock(rq);
+			arg.dest_cpu = select_fallback_rq(cpu, p);
+			task_rq_unlock(rq, p, &rf);
 
 			unpin_current_cpu();
 			preempt_lazy_enable();
-- 
2.24.1