linux-kernel - Re: [PATCH 4/4] cpu/hotplug: Fix CPU down rollback

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Message-ID: <YAmWP1vbLYFgl82n@hirez.programming.kicks-ass.net>
Date:   Thu, 21 Jan 2021 15:57:03 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     vincent.donnefort@....com
Cc:     tglx@...utronix.de, linux-kernel@...r.kernel.org,
        valentin.schneider@....com
Subject: Re: [PATCH 4/4] cpu/hotplug: Fix CPU down rollback

On Mon, Jan 11, 2021 at 05:10:47PM +0000, vincent.donnefort@....com wrote:
> From: Vincent Donnefort <vincent.donnefort@....com>
> 
> After the AP brought itself down to CPUHP_TEARDOWN_CPU, the BP will finish
> the job. The steps left are as followed:
> 
>    +--------------------+
>    | CPUHP_TEARDOWN_CPU |  -> If fails state is CPUHP_TEARDOWN_CPU
>    +--------------------+
>    |   ATOMIC STATES    |  -> Cannot Fail
>    +--------------------+
>    |  CPUHP_BRINGUP_CPU |  -> Cannot fail
>    +--------------------+
>    |        ...         |
>    |        ...         |  -> Can fail and rollback

These are the PREPARE/DEAD states, right? It would be _really_ daft for
a DEAD notifier to fail. But yeah, I suppose that if it does, it will
indeed end up in CPUHP_AP_ONLINE_IDLE.

Do we want to WARN when a DEAD notifier fails?