linux-kernel - Re: [PATCH v2] cpu/hotplug: Set st->cpu earlier

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Message-ID: <bc66bee6-7c99-b289-f5e9-ccaf03d5605d@arm.com>
Date:   Tue, 22 Mar 2022 15:59:20 +0000
From:   Vincent Donnefort <vincent.donnefort@....com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Steven Price <steven.price@....com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, Baokun Li <libaokun1@...wei.com>,
        Dongli Zhang <dongli.zhang@...cle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Yuan ZhaoXiong <yuanzhaoxiong@...du.com>,
        YueHaibing <yuehaibing@...wei.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>
Subject: Re: [PATCH v2] cpu/hotplug: Set st->cpu earlier



On 22/03/2022 15:31, Thomas Gleixner wrote:
> On Wed, Mar 16 2022 at 15:36, Steven Price wrote:
>> Setting the 'cpu' member of struct cpuhp_cpu_state in cpuhp_create() is
>> too late as other callbacks can be made before that point.
> 
> What?
> 
>          CPUHP_OFFLINE = 0,
>          CPUHP_CREATE_THREADS,
> 
> The create threads callback is the very first callback which is invoked
> for a to be plugged CPU on the control CPU. So which earlier callback
> can be invoked and fail?
> 
> Thanks,
> 
>          tglx


CPUHP_CREATE_THREADS itself can fail, before st->cpu is set. Also, that 
value is used outside of the callbacks (cpuhp_set_state() in _cpu_up()).

But indeed this description could be refined a bit.