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

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Message-ID: <d1255075-e273-a74d-3bc7-d97b320470db@redhat.com>
Date:   Tue, 25 Aug 2020 19:32:40 -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 6:26 PM, Waiman Long wrote:
> 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? 

Or if you can make the to-be-offlined cpu free the debugobjs before it 
is offlined. That will work too.

Cheers,
Longman