[PATCH 1/2] sched/core: Fixed missing rq clock update before calling set_rq_offline()

[Hao Jia]

This is triggered during cpu offline when CONFIG_CPU_FREQ is enabled:

------------[ cut here ]------------
rq->clock_update_flags < RQCF_ACT_SKIP
WARNING: CPU: 24 PID: 754 at kernel/sched/sched.h:1496
enqueue_top_rt_rq+0x139/0x160
Call Trace:
 <TASK>
 ? intel_pstate_update_util+0x3b0/0x3b0
 rq_offline_rt+0x1b7/0x250
 set_rq_offline.part.120+0x28/0x60
 rq_attach_root+0xc4/0xd0
 cpu_attach_domain+0x3dc/0x7f0
 ? __schedule+0x65e/0x1310
 partition_sched_domains_locked+0x2a5/0x3c0
 rebuild_sched_domains_locked+0x477/0x830
 ? percpu_rwsem_wait+0x140/0x140
 rebuild_sched_domains+0x1b/0x30
 cpuset_hotplug_workfn+0x2ca/0xc90
 ? balance_push+0x56/0x120
 ? _raw_spin_unlock+0x15/0x30
 ? finish_task_switch+0x98/0x2f0
 ? __switch_to+0x116/0x410
 ? __schedule+0x65e/0x1310 ? internal_add_timer+0x42/0x60
 ? _raw_spin_unlock_irqrestore+0x23/0x40
 ? add_timer_on+0xd5/0x130
 process_one_work+0x1bc/0x3d0
 worker_thread+0x4c/0x380
 ? preempt_count_add+0x56/0xa0
 ? rescuer_thread+0x310/0x310
 kthread+0xe6/0x110
 ? kthread_complete_and_exit+0x20/0x20
 ret_from_fork+0x1f/0x30

Before calling set_rq_offline() we need to update the rq clock to avoid
using the old rq clock, and use rq_lock_irqsave()/rq_unlock_irqrestore()
to replace raw_spin_rq_lock_irqsave()/raw_spin_rq_unlock_irqrestore() to
ensure that rq->clock_update_flags are cleared before updating the rq
clock.

Steps to reproduce:
1. Enable CONFIG_SMP and CONFIG_CPU_FREQ when compiling the kernel
2. echo 1 > /sys/kernel/debug/clear_warn_once
3. cpupower -c all frequency-set -g powersave
4. Run some rt tasks e.g. Create 5*n rt (100% running) tasks (on a
   system with n CPUs)
5. Offline cpu one by one until the warninng is triggered

Signed-off-by: Hao Jia <jiahao.os@xxxxxxxxxxxxx>
---
 kernel/sched/topology.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 051aaf65c749..017f7583f0e2 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -487,15 +487,17 @@ static void free_rootdomain(struct rcu_head *rcu)
 void rq_attach_root(struct rq *rq, struct root_domain *rd)
 {
 	struct root_domain *old_rd = NULL;
-	unsigned long flags;
+	struct rq_flags rf;
 
-	raw_spin_rq_lock_irqsave(rq, flags);
+	rq_lock_irqsave(rq, &rf);
 
 	if (rq->rd) {
 		old_rd = rq->rd;
 
-		if (cpumask_test_cpu(rq->cpu, old_rd->online))
+		if (cpumask_test_cpu(rq->cpu, old_rd->online)) {
+			update_rq_clock(rq);
 			set_rq_offline(rq);
+		}
 
 		cpumask_clear_cpu(rq->cpu, old_rd->span);
 
@@ -515,7 +517,7 @@ void rq_attach_root(struct rq *rq, struct root_domain *rd)
 	if (cpumask_test_cpu(rq->cpu, cpu_active_mask))
 		set_rq_online(rq);
 
-	raw_spin_rq_unlock_irqrestore(rq, flags);
+	rq_unlock_irqrestore(rq, &rf);
 
 	if (old_rd)
 		call_rcu(&old_rd->rcu, free_rootdomain);
-- 
2.37.0