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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 08:47:41 -0500
Message-Id: <6D3E70AC-8D01-41C7-9FDE-6693E9706425@joelfernandes.org>
References: <Y8qazpmqk4dmw37F@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: <Y8qazpmqk4dmw37F@kroah.com>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Precedence: bulk


> On Jan 20, 2023, at 8:44 AM, Greg Kroah-Hartman <gregkh@linuxfoundation.or=
g> wrote:
>=20
> =EF=BB=BFOn Fri, Jan 20, 2023 at 08:32:30AM -0500, Joel Fernandes wrote:
>>=20
>>=20
>>>> On Jan 20, 2023, at 2:05 AM, Greg Kroah-Hartman <gregkh@linuxfoundation=
.org> wrote:
>>>=20
>>> =EF=BB=BFOn Thu, Jan 19, 2023 at 08:44:35PM +0000, Joel Fernandes (Googl=
e) 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 c=
auses
>>>> torture tests that do offlining to end up trying to offline this CPU ca=
using
>>>> test failures. Such failure happens on all architectures.
>>>>=20
>>>> Fix it by asking the opinion of the nohz subsystem on whether the CPU c=
an
>>>> 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 re=
st of the kernel")
>>>> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
>>>=20
>>> Also want to cc: stable on the patch?
>>=20
>> 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?
>=20
> As per the rules we have had for the last 15+ years, always add a cc:
> stable to be sure that the patch will be considered for stable releases.
> If not, you are on you own and sometimes we might notice it, others not.
>=20
> See:
>    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html=

> for the details.

Ah my bad, I did read that already but somehow assumed anything merged with a=
 Fixes tag was already considered for stable. I will always Cc stable hencef=
orth if I want something in stable.

Thank you!

 - Joel


>=20
> thanks,
>=20
> greg k-h