linux-kernel - Re: 回复: [PATCH] debugobjects: install cpu hotplug callback

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Message-ID: <e75c1601-b466-8476-f75b-514b1c21646e@redhat.com>
Date:   Tue, 25 Aug 2020 18:26:29 -0400
From:   Waiman Long <longman@...hat.com>
To:     "Zhang, Qiang" <Qiang.Zhang@...driver.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "elver@...gle.com" <elver@...gle.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: 回复: [PATCH] debugobjects: install cpu hotplug callback

On 8/25/20 12:53 AM, Zhang, Qiang wrote:
> ________________________________________
> 发件人: linux-kernel-owner@...r.kernel.org <linux-kernel-owner@...r.kernel.org> 代表 qiang.zhang@...driver.com <qiang.zhang@...driver.com>
> 发送时间: 2020年8月20日 11:24
> 收件人: tglx@...utronix.de; elver@...gle.com; longman@...hat.com
> 抄送: linux-kernel@...r.kernel.org
> 主题: [PATCH] debugobjects: install cpu hotplug callback
>
> From: Zqiang <qiang.zhang@...driver.com>
>
> When a cpu going offline, we should free objects in "percpu_obj_pool"
> free_objs list which corresponding to this cpu.

The percpu free object pool is supposed to be accessed only by that 
particular cpu without any lock. Trying to access it from another cpu 
can cause a race condition unless one can make sure that the offline cpu 
won't become online in the mean time. There shouldn't be too many free 
objects in the percpu pool. Is it worth the effort to free them?

Cheers,
Longman