linux-kernel - Re: [PATCH] tick/nohz: Fix cpu_is_hotpluggable() by checking with nohz subsystem

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Message-Id: <37171A49-82E9-4008-9B5B-1CEEDC9B653E@joelfernandes.org>
Date:   Fri, 20 Jan 2023 08:32:30 -0500
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org,
        Frederic Weisbecker <frederic@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Zhouyi Zhou <zhouzhouyi@...il.com>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        rcu <rcu@...r.kernel.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] tick/nohz: Fix cpu_is_hotpluggable() by checking with nohz subsystem



> On Jan 20, 2023, at 2:05 AM, Greg Kroah-Hartman <gregkh@...uxfoundation.org> wrote:
> 
> On Thu, Jan 19, 2023 at 08:44:35PM +0000, Joel Fernandes (Google) wrote:
>> For CONFIG_NO_HZ_FULL systems, the tick_do_timer_cpu cannot be offlined.
>> However, cpu_is_hotpluggable() still returns true for those CPUs. This causes
>> torture tests that do offlining to end up trying to offline this CPU causing
>> test failures. Such failure happens on all architectures.
>> 
>> Fix it by asking the opinion of the nohz subsystem on whether the CPU can
>> be hotplugged.
>> 
>> [ Apply Frederic Weisbecker feedback on refactoring tick_nohz_cpu_down(). ]
>> 
>> Cc: Frederic Weisbecker <frederic@...nel.org>
>> Cc: "Paul E. McKenney" <paulmck@...nel.org>
>> Cc: Zhouyi Zhou <zhouzhouyi@...il.com>
>> Cc: Will Deacon <will@...nel.org>
>> Cc: Marc Zyngier <maz@...nel.org>
>> Cc: rcu <rcu@...r.kernel.org>
>> Fixes: 2987557f52b9 ("driver-core/cpu: Expose hotpluggability to the rest of the kernel")
>> Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> 
> Also want to cc: stable on the patch?

Oh sure, sorry. For some reason I thought Sasha and your AI scripts were looking at the Linux-kernel list as well. Or are they, and a Cc to stable is just to be doubly sure?

> Anyway, for the driver core portion:

Thanks!

 - Joel

> 
> Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>