linux-kernel - Re: [PATCH] [RFC] rt: kernel/sched/core: fix kthread_park() pending too long when CPU un-plugged

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Message-ID: <X/bmU4byS7k46zWM@hirez.programming.kicks-ass.net>
Date:   Thu, 7 Jan 2021 11:45:39 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ran Wang <ran.wang_1@....com>
Cc:     Sebastian Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jiafei Pan <jiafei.pan@....com>,
        linux-rt-users@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [RFC] rt: kernel/sched/core: fix kthread_park() pending
 too long when CPU un-plugged

On Thu, Jan 07, 2021 at 05:18:41PM +0800, Ran Wang wrote:
> +
> +			if (IS_ENABLED(CONFIG_PREEMPT_RT) &&
> +			    !strncmp(p->comm, "ksoftirqd/", 10))
> +				schedule_hrtimeout(&to,
> +					HRTIMER_MODE_REL | HRTIMER_MODE_HARD);
> +			else
> +				schedule_hrtimeout(&to, HRTIMER_MODE_REL);

This is horrific, why did you not self-censor and spare me the mental
anguish of having to formulate a CoC compliant response?

It also violates coding style, but given the total lack of any sense,
that seems like a minor detail.

Why can't we use HRTIMER_MODE_HARD unconditionally?