linux-kernel - [PATCH 2/6] sched: Verify some SMP assumptions

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Date:   Mon, 15 Jun 2020 14:56:56 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     mingo@...nel.org, tglx@...utronix.de
Cc:     linux-kernel@...r.kernel.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        paulmck@...nel.org, frederic@...nel.org, peterz@...radead.org
Subject: [PATCH 2/6] sched: Verify some SMP assumptions

Validate that:
 - __smp_call_single_queue() is only used on remote CPUs
 - task and rq CPUs match on activate_task()

(and always use activate_task() where we should)

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/sched/core.c |    8 ++++----
 kernel/smp.c        |    2 ++
 2 files changed, 6 insertions(+), 4 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1311,6 +1311,8 @@ static inline void dequeue_task(struct r
 
 void activate_task(struct rq *rq, struct task_struct *p, int flags)
 {
+	SCHED_WARN_ON(task_cpu(p) != cpu_of(rq));
+
 	if (task_contributes_to_load(p))
 		rq->nr_uninterruptible--;
 
@@ -1474,8 +1476,7 @@ static struct rq *move_queued_task(struc
 {
 	lockdep_assert_held(&rq->lock);
 
-	WRITE_ONCE(p->on_rq, TASK_ON_RQ_MIGRATING);
-	dequeue_task(rq, p, DEQUEUE_NOCLOCK);
+	deactivate_task(rq, p, DEQUEUE_NOCLOCK);
 	set_task_cpu(p, new_cpu);
 	rq_unlock(rq, rf);
 
@@ -1483,8 +1484,7 @@ static struct rq *move_queued_task(struc
 
 	rq_lock(rq, rf);
 	BUG_ON(task_cpu(p) != new_cpu);
-	enqueue_task(rq, p, 0);
-	p->on_rq = TASK_ON_RQ_QUEUED;
+	activate_task(rq, p, 0);
 	check_preempt_curr(rq, p, 0);
 
 	return rq;
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -135,6 +135,8 @@ static DEFINE_PER_CPU_SHARED_ALIGNED(cal
 
 void __smp_call_single_queue(int cpu, struct llist_node *node)
 {
+	WARN_ON_ONCE(cpu == smp_processor_id());
+
 	/*
 	 * The list addition should be visible before sending the IPI
 	 * handler locks the list to pull the entry off it because of