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From:   Kairui Song <kasong@redhat.com>
Date:   Thu, 7 Mar 2019 13:58:41 +0800
Message-ID: <CACPcB9fWiEcHZ3j2t9++HWe6a_0y2tvO3MbcvB8hDaFXgOmuwA@mail.gmail.com>
Subject: Re: [PATCH v4] x86/gart/kcore: Exclude GART aperture from kcore
To:     Jiri Bohac <jbohac@suse.cz>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Omar Sandoval <osandov@fb.com>, Baoquan He <bhe@redhat.com>,
        Dave Young <dyoung@redhat.com>
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On Thu, Mar 7, 2019 at 1:03 AM Jiri Bohac <jbohac@suse.cz> wrote:
>
> Hi,
>
> On Wed, Mar 06, 2019 at 07:38:59PM +0800, Kairui Song wrote:
> > +int register_mem_pfn_is_ram(int (*fn)(unsigned long pfn))
> > +{
> > +     if (mem_pfn_is_ram)
> > +             return -EBUSY;
> > +     mem_pfn_is_ram = fn;
> > +     return 0;
> > +}
> > +
> > +void unregister_mem_pfn_is_ram(void)
> > +{
> > +     mem_pfn_is_ram = NULL;
> > +}
> > +
> > +static int pfn_is_ram(unsigned long pfn)
> > +{
> > +     if (mem_pfn_is_ram)
> > +             return mem_pfn_is_ram(pfn);
> > +     else
> > +             return 1;
> > +}
> > +
>
> If anyone were ever to use unregister_mem_pfn_is_ram(),
> pfn_is_ram() would become racy.
>
> In V2 you had this:
>         +       fn = mem_pfn_is_ram;
>         +       if (fn)
>         +               ret = fn(pfn);
>
> I agree it's unnecessary since nothing uses
> unregister_mem_pfn_is_ram(). But then I think it would be best to
> just drop the unregister function.
>
> Otherwise the patch looks good to me.
>

Good catch, let me remove the unregister function.
Also, I'd like to have an __init prefix for register_mem_pfn_is_ram,
will update in V5.

--
Best Regards,
Kairui Song