linux-kernel - [PATCH] sched/deadline: Fix missing clock update in migrate_task_rq

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Message-Id: <20210804135925.3734605-1-dietmar.eggemann@arm.com>
Date:   Wed,  4 Aug 2021 15:59:25 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Bruno Goncalves <bgoncalv@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] sched/deadline: Fix missing clock update in migrate_task_rq_dl()

A missing clock update is causing the following warning:

rq->clock_update_flags < RQCF_ACT_SKIP
WARNING: CPU: 112 PID: 2041 at kernel/sched/sched.h:1453
sub_running_bw.isra.0+0x190/0x1a0
...
CPU: 112 PID: 2041 Comm: sugov:112 Tainted: G W 5.14.0-rc1 #1
Hardware name: WIWYNN Mt.Jade Server System
B81.030Z1.0007/Mt.Jade Motherboard, BIOS 1.6.20210526 (SCP:
1.06.20210526) 2021/05/26
...
Call trace:
  sub_running_bw.isra.0+0x190/0x1a0
  migrate_task_rq_dl+0xf8/0x1e0
  set_task_cpu+0xa8/0x1f0
  try_to_wake_up+0x150/0x3d4
  wake_up_q+0x64/0xc0
  __up_write+0xd0/0x1c0
  up_write+0x4c/0x2b0
  cppc_set_perf+0x120/0x2d0
  cppc_cpufreq_set_target+0xe0/0x1a4 [cppc_cpufreq]
  __cpufreq_driver_target+0x74/0x140
  sugov_work+0x64/0x80
  kthread_worker_fn+0xe0/0x230
  kthread+0x138/0x140
  ret_from_fork+0x10/0x18

The task causing this is the `cppc_fie` DL task introduced by
commit 1eb5dde674f5 ("cpufreq: CPPC: Add support for frequency
invariance").

With CONFIG_ACPI_CPPC_CPUFREQ_FIE=y and schedutil cpufreq governor on
slow-switching system (like on this Ampere Altra WIWYNN Mt. Jade Arm
Server):

DL task `curr=sugov:112` lets `p=cppc_fie` migrate and since the latter
is in `non_contending` state, migrate_task_rq_dl() calls

  sub_running_bw()->__sub_running_bw()->cpufreq_update_util()->
  rq_clock()->assert_clock_updated()

on p.

Fix this by updating the clock for a non_contending task in
migrate_task_rq_dl() before calling sub_running_bw().

Reported-by: Bruno Goncalves <bgoncalv@...hat.com>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@....com>
---
 kernel/sched/deadline.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index aaacd6cfd42f..4920f498492f 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1733,6 +1733,7 @@ static void migrate_task_rq_dl(struct task_struct *p, int new_cpu __maybe_unused
 	 */
 	raw_spin_rq_lock(rq);
 	if (p->dl.dl_non_contending) {
+		update_rq_clock(rq);
 		sub_running_bw(&p->dl, &rq->dl);
 		p->dl.dl_non_contending = 0;
 		/*
-- 
2.25.1