linux-kernel - Re: [PATCH v2 1/2] cpu/hotplug: introduce 'num_dying

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Message-ID: <87bkjv1oq5.ffs@tglx>
Date:   Mon, 10 Apr 2023 22:12:02 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ye Bin <yebin@...weicloud.com>, dennis@...nel.org, tj@...nel.org,
        cl@...ux.com, linux-mm@...ck.org, yury.norov@...il.com,
        andriy.shevchenko@...ux.intel.com, linux@...musvillemoes.dk
Cc:     linux-kernel@...r.kernel.org, dchinner@...hat.com,
        yebin10@...wei.com, yebin@...weicloud.com
Subject: Re: [PATCH v2 1/2] cpu/hotplug: introduce 'num_dying_cpus' to get
 dying CPUs count

On Thu, Apr 06 2023 at 09:56, Ye Bin wrote:
> From: Ye Bin <yebin10@...wei.com>
>
> Introduce '__num_dying_cpus' variable to cache the number of dying CPUs
> in the core and just return the cached variable.

Why?

That atomic counter is racy too if read and acted upon w/o having CPUs
read locked.

All it does is making the race window smaller vs. the cpumask_weight()
based implementation. It's still racy and incorrect.

So no, this is not going to happen.

Thanks,

        tglx