Re: [PATCH] sched/deadline: Fix missing clock update in migrate_task_rq_dl()

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Aug 05, 2021 at 10:16:26AM +0200, Daniel Bristot de Oliveira wrote:
> On 8/4/21 3:59 PM, Dietmar Eggemann wrote:
> > 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@redhat.com>
> > Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
> 
> Reviewed-by: Daniel Bristot de Oliveira <bristot@kernel.org>

Thanks!