linux-kernel - Re: [PATCH v2] sched/core: fix illegal RCU from offline CPUs

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Date:   Thu, 23 Jan 2020 23:21:35 -0500
From:   Qian Cai <cai@....pw>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        paulmck@...nel.org, tglx@...utronix.de, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched/core: fix illegal RCU from offline CPUs

> On Jan 21, 2020, at 5:35 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> Something like this; except you'll need to go audit archs to make sure
> they all call idle_task_exit() and/or put in comments on why they don't
> have to (perhaps their bringup switches them to &init_mm unconditionally
> and the switch_mm() is not required).

Damn, I am having a hard time to motivate myself to learn all about those two “dead“ arches from scratch. I suppose the first step we could put a dummy finish_cpu() for alpha and parisc if they don’t call idle_task_exit() in the first place anyway, so if it is a bug there it is another issue that could be dealt with in a separate patch later?