linux-kernel - Re: [PATCH] cpufreq: Avoid leaving stale IRQ work items during CPU offline

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Date:   Thu, 12 Dec 2019 17:49:54 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Peng Fan <peng.fan@....com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Anson Huang <anson.huang@....com>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH] cpufreq: Avoid leaving stale IRQ work items during CPU offline

On Wed, Dec 11, 2019 at 2:53 PM Peng Fan <peng.fan@....com> wrote:
>
> > Subject: [PATCH] cpufreq: Avoid leaving stale IRQ work items during CPU
> > offline
> >
> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> >
> > The scheduler code calling cpufreq_update_util() may run during CPU offline
> > on the target CPU after the IRQ work lists have been flushed for it, so the
> > target CPU should be prevented from running code that may queue up an IRQ
> > work item on it at that point.
> >
> > Unfortunately, that may not be the case if dvfs_possible_from_any_cpu is set
> > for at least one cpufreq policy in the system, because that allows the CPU
> > going offline to run the utilization update callback of the cpufreq governor on
> > behalf of another (online) CPU in some cases.
> >
> > If that happens, the cpufreq governor callback may queue up an IRQ work on
> > the CPU running it, which is going offline, and the IRQ work will not be flushed
>
> "will" -> "might"

Well, I'm not sure, but OK.