linux-kernel - Re: [RFC PATCH] kernel/cpu: restart cpu

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Message-ID: <d0bf78a2-8bba-825e-89de-d41568ae2793@redhat.com>
Date:   Thu, 21 Apr 2022 16:34:05 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Joel Savitz <jsavitz@...hat.com>, linux-kernel@...r.kernel.org
Cc:     Valentin Schneider <valentin.schneider@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Yuan ZhaoXiong <yuanzhaoxiong@...du.com>,
        Baokun Li <libaokun1@...wei.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        YueHaibing <yuehaibing@...wei.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        David Hildenbrand <dhildenb@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [RFC PATCH] kernel/cpu: restart cpu_up when hotplug is disabled

On 21.04.22 16:31, David Hildenbrand wrote:
>>> It's far from perfect I would say, but we really wanted to avoid
>>> letting user space having to deal with retry logic.
>>
>> What's so hard with retry logic in user space? 
>>
>> If you can come up with a reasonable argument why user space cannot be
>> fixed, then there is certainly a better solution than slapping a
>> msleep(5) at some random place into the code.
> Most probably you're right and we should just retry in udev. Staring at
> the history, it looks like the -EBUSY might have been returned forever,
> so user space just never really triggered it on actual CPU hotplug
> because it doesn't usually happen that cpu hotplug is disabled.

The last part was confusing: "on actual CPU hotplug because it doesn't
usually happen that cpu hotplug is disabled when onlining a CPU that was
just hotplugged."

-- 
Thanks,

David / dhildenb