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

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Message-ID: <eedc945f-2d48-1dcf-30f3-21e2e1b094f9@redhat.com>
Date:   Tue, 25 Aug 2020 20:48:53 -0400
From:   Waiman Long <longman@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        "Zhang, Qiang" <Qiang.Zhang@...driver.com>,
        "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 7:53 PM, Thomas Gleixner wrote:
> On Tue, Aug 25 2020 at 18:26, Waiman Long wrote:
>> On 8/25/20 12:53 AM, Zhang, Qiang wrote:
>>> 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.
> It is actually safe because CPU hotplug is globally serialized and there
> is no way that an offline CPU will come back from death valley
> magically. If such a zombie ever surfaces then we have surely more
> serious problems than accessing that pool :)

Thanks for the clarification. I haven't looked into where the callback 
functions are being called so I am not 100% sure.

Cheers,
Longman