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From:   Joel Fernandes <joel@joelfernandes.org>
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Subject: Re: [PATCH] tick/nohz: Fix cpu_is_hotpluggable() by checking with nohz subsystem
Date:   Fri, 20 Jan 2023 08:32:30 -0500
Message-Id: <37171A49-82E9-4008-9B5B-1CEEDC9B653E@joelfernandes.org>
References: <Y8o9Mh1ktK0jdQy9@kroah.com>
Cc:     linux-kernel@vger.kernel.org,
        Frederic Weisbecker <frederic@kernel.org>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Zhouyi Zhou <zhouzhouyi@gmail.com>,
        Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
        rcu <rcu@vger.kernel.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Ingo Molnar <mingo@kernel.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>
In-Reply-To: <Y8o9Mh1ktK0jdQy9@kroah.com>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Precedence: bulk


> On Jan 20, 2023, at 2:05 AM, Greg Kroah-Hartman <gregkh@linuxfoundation.or=
g> wrote:
>=20
> =EF=BB=BFOn 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 ca=
uses
>> torture tests that do offlining to end up trying to offline this CPU caus=
ing
>> test failures. Such failure happens on all architectures.
>>=20
>> Fix it by asking the opinion of the nohz subsystem on whether the CPU can=

>> be hotplugged.
>>=20
>> [ Apply Frederic Weisbecker feedback on refactoring tick_nohz_cpu_down().=
 ]
>>=20
>> Cc: Frederic Weisbecker <frederic@kernel.org>
>> Cc: "Paul E. McKenney" <paulmck@kernel.org>
>> Cc: Zhouyi Zhou <zhouzhouyi@gmail.com>
>> Cc: Will Deacon <will@kernel.org>
>> Cc: Marc Zyngier <maz@kernel.org>
>> Cc: rcu <rcu@vger.kernel.org>
>> Fixes: 2987557f52b9 ("driver-core/cpu: Expose hotpluggability to the rest=
 of the kernel")
>> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
>=20
> Also want to cc: stable on the patch?

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

> Anyway, for the driver core portion:

Thanks!

 - Joel

>=20
> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>