linux-kernel - Re: [PATCH v4 4/4] sched/core: Avoid multiple calling update_rq_clock() in unthrottle_offline_cfs

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Message-ID: <xm26zg59acky.fsf@google.com>
Date:   Thu, 08 Jun 2023 14:06:21 -0700
From:   Benjamin Segall <bsegall@...gle.com>
To:     Hao Jia <jiahao.os@...edance.com>
Cc:     mingo@...hat.com, peterz@...radead.org, mingo@...nel.org,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com,
        mgorman@...hsingularity.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 4/4] sched/core: Avoid multiple calling
 update_rq_clock() in unthrottle_offline_cfs_rqs()

Hao Jia <jiahao.os@...edance.com> writes:

> This WARN_DOUBLE_CLOCK warning is triggered during cpu offline.
> ------------[ cut here ]------------
> rq->clock_update_flags & RQCF_UPDATED
> WARNING: CPU: 0 PID: 3323 at kernel/sched/core.c:741
> update_rq_clock+0xaf/0x180
> Call Trace:
>  <TASK>
>  unthrottle_cfs_rq+0x4b/0x300
>  rq_offline_fair+0x89/0x90
>  set_rq_offline.part.118+0x28/0x60
>  rq_attach_root+0xc4/0xd0
>  cpu_attach_domain+0x3dc/0x7f0
>  partition_sched_domains_locked+0x2a5/0x3c0
>  rebuild_sched_domains_locked+0x477/0x830
>  rebuild_sched_domains+0x1b/0x30
>  cpuset_hotplug_workfn+0x2ca/0xc90
>  ? balance_push+0x56/0xf0
>  ? _raw_spin_unlock+0x15/0x30
>  ? finish_task_switch+0x98/0x2f0
>  ? __switch_to+0x291/0x410
>  ? __schedule+0x65e/0x1310
>  process_one_work+0x1bc/0x3d0
>  worker_thread+0x4c/0x380
>  ? preempt_count_add+0x92/0xa0
>  ? rescuer_thread+0x310/0x310
>  kthread+0xe6/0x110
>  ? kthread_complete_and_exit+0x20/0x20
>  ret_from_fork+0x1f/0x30
>
> The rq clock has been updated before the set_rq_offline()
> function runs, so we don't need to call update_rq_clock() in
> unthrottle_offline_cfs_rqs().

I don't think we do in the path from rq_attach_root (though that's easy
enough to fix, of course).