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Message-ID: <ca667dd9-f228-c6a8-390b-7e3abde391c4@redhat.com>
Date:   Thu, 21 Apr 2022 16:31:13 +0200
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Subject: Re: [RFC PATCH] kernel/cpu: restart cpu_up when hotplug is disabled
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To:     Thomas Gleixner <tglx@linutronix.de>,
        Joel Savitz <jsavitz@redhat.com>, linux-kernel@vger.kernel.org
Cc:     Valentin Schneider <valentin.schneider@arm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Frederic Weisbecker <frederic@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Yuan ZhaoXiong <yuanzhaoxiong@baidu.com>,
        Baokun Li <libaokun1@huawei.com>,
        "Jason A. Donenfeld" <Jason@zx2c4.com>,
        YueHaibing <yuehaibing@huawei.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        David Hildenbrand <dhildenb@redhat.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>
References: <20220418195402.2986573-1-jsavitz@redhat.com>
 <d98bb24d-b8cd-b00b-57c3-d96dae57ad5b@redhat.com> <877d7itszm.ffs@tglx>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <877d7itszm.ffs@tglx>
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>> 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.

-- 
Thanks,

David / dhildenb