linux-kernel - Re: [PATCH] tick: Remove unreasonable detached state set in tick

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Message-ID: <77b00eac-8dd5-23bc-a44c-3c3621b7c62a@loongson.cn>
Date: Wed, 3 Sep 2025 17:36:05 +0800
From: Bibo Mao <maobibo@...ngson.cn>
To: Frederic Weisbecker <frederic@...nel.org>
Cc: Anna-Maria Behnsen <anna-maria@...utronix.de>,
 Ingo Molnar <mingo@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tick: Remove unreasonable detached state set in
 tick_shutdown()



On 2025/9/2 下午10:07, Frederic Weisbecker wrote:
> Le Thu, Aug 07, 2025 at 11:59:54AM +0800, Bibo Mao a écrit :
>> Function clockevents_switch_state() will check whether it has already
>> switched to specified state, do nothing if it has.
>>
>> In function tick_shutdown(), it will set detached state at first and
>> call clockevents_switch_state() in clockevents_exchange_device(). The
>> function clockevents_switch_state() will do nothing since it is already
>> detached state. So the tick timer device will not be shutdown when CPU
>> is offline. In guest VM system, timer interrupt will prevent vCPU to sleep
>> if vCPU is hot removed.
>>
>> Here remove state set before calling clockevents_exchange_device(),
>> its state will be set in function clockevents_switch_state() if it
>> succeeds to do so.
>>
>> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
> 
> On a second thought, it may need the following tags:
> 
> Fixes: bf9a001fb8e4 ("clocksource/drivers/timer-tegra: Remove clockevents shutdown call on offlining")
> Fixes: cd165ce8314f ("clocksource/drivers/qcom: Remove clockevents shutdown call on offlining")
> Fixes: 30f8c70a85bc ("clocksource/drivers/armada-370-xp: Remove clockevents shutdown call on offlining")
> Fixes: ba23b6c7f974 ("clocksource/drivers/exynos_mct: Remove clockevents shutdown call on offlining")
> Fixes: 15b810e0496e ("clocksource/drivers/arm_global_timer: Remove clockevents shutdown call on offlining")
> Fixes: 78b5c2ca5f27 ("clocksource/drivers/arm_arch_timer: Remove clockevents shutdown call on offlining")
> Fixes: 900053d9eedf ("ARM: smp_twd: Remove clockevents shutdown call on offlining")
> 
> Because those commits removed shutdown calls made from drivers that assumed the
> core would do on their behalf. But it was not the case before your fix.
Ok, will add these fixes tags in next version.

Regards
Bibo Mao
> 
> Thanks!
>