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From: Thomas Gleixner <tglx@linutronix.de>
To: Ye Bin <yebin@huaweicloud.com>,
	dennis@kernel.org, tj@kernel.org, cl@linux.com,
	linux-mm@kvack.org, yury.norov@gmail.com,
	andriy.shevchenko@linux.intel.com, linux@rasmusvillemoes.dk
Cc: linux-kernel@vger.kernel.org, dchinner@redhat.com,
	yebin10@huawei.com, yebin@huaweicloud.com
Subject: Re: [PATCH v2 1/2] cpu/hotplug: introduce 'num_dying_cpus' to get dying CPUs count
Date: Mon, 10 Apr 2023 22:12:02 +0200	[thread overview]
Message-ID: <87bkjv1oq5.ffs@tglx> (raw)
In-Reply-To: <20230406015629.1804722-2-yebin@huaweicloud.com>

On Thu, Apr 06 2023 at 09:56, Ye Bin wrote:
> From: Ye Bin <yebin10@huawei.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




  parent reply	other threads:[~2023-04-10 20:12 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-04-06  1:56 [PATCH v2 0/2] fix dying cpu compare race Ye Bin
2023-04-06  1:56 ` [PATCH v2 1/2] cpu/hotplug: introduce 'num_dying_cpus' to get dying CPUs count Ye Bin
2023-04-10 17:42   ` Yury Norov
2023-04-10 20:12   ` Thomas Gleixner [this message]
2023-04-06  1:56 ` [PATCH v2 2/2] lib/percpu_counter: fix dying cpu compare race Ye Bin
2023-04-08  7:13   ` Dennis Zhou
2023-04-10 20:53   ` Thomas Gleixner
2023-04-11  6:56     ` Thomas Gleixner

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