linux-kernel - Re: [PATCH] Documentation/no_hz: Remove description that states boot CPU cannot be nohz

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Message-ID: <2025020547-judo-precise-0b3c@gregkh>
Date: Wed, 5 Feb 2025 10:18:17 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: Krishanth.Jagaduri@...y.com
Cc: Thomas Gleixner <tglx@...utronix.de>, Jonathan Corbet <corbet@....net>,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	Atsushi Ochiai <Atsushi.Ochiai@...y.com>,
	Daniel Palmer <Daniel.Palmer@...y.com>,
	Oleg Nesterov <oleg@...hat.com>, stable@...r.kernel.org
Subject: Re: [PATCH] Documentation/no_hz: Remove description that states boot
 CPU cannot be nohz_full

On Wed, Feb 05, 2025 at 08:32:14AM +0530, Krishanth Jagaduri via B4 Relay wrote:
> From: Oleg Nesterov <oleg@...hat.com>
> 
> [ Upstream commit 5097cbcb38e6e0d2627c9dde1985e91d2c9f880e ]

It's just the documentation part of that commit, not the full one.

> Documentation/timers/no_hz.rst states that the "nohz_full=" mask must not
> include the boot CPU, which is no longer true after:
> 
>   commit 08ae95f4fd3b ("nohz_full: Allow the boot CPU to be nohz_full").
> 
> Apply changes only to Documentation/timers/no_hz.rst in stable kernels.

You dropped the rest of the changelog text here :(

> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> Cc: stable@...r.kernel.org # 5.4+
> Signed-off-by: Krishanth Jagaduri <Krishanth.Jagaduri@...y.com>

And you dropped all the other signed-off-by lines :(

> ---
> Hi,
> 
> Before kernel 6.9, Documentation/timers/no_hz.rst states that
> "nohz_full=" mask must not include the boot CPU, which is no longer
> true after commit 08ae95f4fd3b ("nohz_full: Allow the boot CPU to be
> nohz_full").
> 
> This was fixed upstream by commit 5097cbcb38e6 ("sched/isolation: Prevent
> boot crash when the boot CPU is nohz_full").
> 
> While it fixes the document description, it also fixes issue introduced
> by another commit aae17ebb53cd ("workqueue: Avoid using isolated cpus'
> timers on queue_delayed_work").
> 
> It is unlikely that it will be backported to stable kernels which does
> not contain the commit that introduced the issue.
> 
> Could Documentation/timers/no_hz.rst be fixed in stable kernels 5.4+?

Does the documentation lines really matter here?

At the very least, we can't take this as the signed-off-by lines are all
gone.  Please resend with them all back, and then make a note that you
are only including the documentation portion and why.

thanks,

greg k-h