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

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Message-ID: <aLb6NFWw3CP2MYp-@localhost.localdomain>
Date: Tue, 2 Sep 2025 16:07:48 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: Bibo Mao <maobibo@...ngson.cn>
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()

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.

Thanks!

-- 
Frederic Weisbecker
SUSE Labs