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Subject: Re: [PATCH] cpu/hotplug: Fix rollback during error-out in
 takedown_cpu()
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     josh@joshtriplett.org, peterz@infradead.org, mingo@kernel.org,
        jiangshanlai@gmail.com, dzickus@redhat.com,
        brendan.jackman@arm.com, malat@debian.org,
        linux-kernel@vger.kernel.org, sramana@codeaurora.org,
        linux-arm-msm@vger.kernel.org
References: <1536042803-6152-1-git-send-email-neeraju@codeaurora.org>
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 <alpine.DEB.2.21.1809051514070.1416@nanos.tec.linutronix.de>
From:   Neeraj Upadhyay <neeraju@codeaurora.org>
Message-ID: <9cac90ff-1a43-8663-da2e-7191975b5e93@codeaurora.org>
Date:   Thu, 6 Sep 2018 08:26:20 +0530
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On 09/05/2018 06:47 PM, Thomas Gleixner wrote:
> On Wed, 5 Sep 2018, Neeraj Upadhyay wrote:
>> On 09/05/2018 05:53 PM, Thomas Gleixner wrote:
>>> And looking closer this is a general issue. Just that the TEARDOWN state
>>> makes it simple to observe. It's universaly broken, when the first teardown
>>> callback fails because, st->state is only decremented _AFTER_ the callback
>>> returns success, but undo_cpu_down() increments unconditionally.
>>>
>> As per my understanding, there are 2 problems here; one is fixed with your
>> patch, and other is cpuhp_reset_state() is used during rollback from non-AP to
>> AP state, which seem to result in 2 increments of st->state (one increment
>> done by cpuhp_reset_state() and another by cpu_thread_fun()) .
> And how did your hack fix that up magically? I'll have a look later today.
>
> Thanks,
>
> 	tglx

The hack fixes it by not calling cpuhp_reset_state() and doing rollback 
state reset inline in  _cpu_down().


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