linux-kernel - Re: [PATCH 02/13] kernel/cpu: Add support for declaring CPU hotplug not supported

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Message-ID: <20231011130743.mdfi27pdwktefbsv@box.shutemov.name>
Date:   Wed, 11 Oct 2023 16:07:43 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        kexec@...ts.infradead.org, linux-coco@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/13] kernel/cpu: Add support for declaring CPU hotplug
 not supported

On Tue, Oct 10, 2023 at 06:35:59AM -0700, Kuppuswamy Sathyanarayanan wrote:
> 
> 
> On 10/5/2023 6:13 AM, Kirill A. Shutemov wrote:
> > The function cpu_hotplug_not_supported() can be called to indicate that
> > CPU hotplug should be disabled. It does not prevent the initial bring up
> > of the CPU, but it stops subsequent offlining.
> > 
> > This function is intended to replace CC_ATTR_HOTPLUG_DISABLED.
> > 
> 
> Looks good to me.
> 
> Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>

Thanks.

> > @@ -543,6 +546,18 @@ static void lockdep_release_cpus_lock(void)
> >  	rwsem_release(&cpu_hotplug_lock.dep_map, _THIS_IP_);
> >  }
> >  
> > +/*
> > + * Declare CPU hotplug not supported.
> > + *
> > + * It doesn't prevent initial bring up of the CPU, but stops offlining.
> > + */
> > +void cpu_hotplug_not_supported(void)
> > +{
> > +	cpu_maps_update_begin();
> > +	cpu_hotplug_supported = false;
> > +	cpu_maps_update_done();
> > +}
> 
> Since this function is not used in this patch, do you need to add __maybe_unused to
> avoid warnings?

Hm? I don't think compiler complains about non-static unused functions. It
has no visibility if it is used.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov