linux-kernel - Re: [PATCH] lib/test_kho: Check if KHO is enabled

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Message-ID: <CA+CK2bB+EpZg7MTKZhFtaGoYfLN5JNeaH9HDv_Avq9Qm+3e2ig@mail.gmail.com>
Date: Fri, 7 Nov 2025 06:15:37 -0500
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: Pratyush Yadav <pratyush@...nel.org>
Cc: akpm@...ux-foundation.org, rppt@...nel.org, graf@...zon.com, 
	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org, linux-mm@...ck.org
Subject: Re: [PATCH] lib/test_kho: Check if KHO is enabled

On Fri, Nov 7, 2025 at 5:24 AM Pratyush Yadav <pratyush@...nel.org> wrote:
>
> On Thu, Nov 06 2025, Pasha Tatashin wrote:
>
> > We must check whether KHO is enabled prior to issuing KHO commands,
> > otherwise KHO internal data structures are not initialized.
>
> Should we have this check in the KHO APIs instead? This check is easy
> enough to miss.

I considered adding a kho_is_enabled() check to every KHO API, but it
seems unnecessary.

In-kernel users of KHO, like reserve_mem and the upcoming LUO, are
already expected to check if KHO is enabled before doing extra
preservation work. I anticipate any future in-kernel users will follow
the same pattern.

We could add a WARN_ON(!kho_is_enabled()) to the internal API calls,
but I don't think it's needed. We already catch this condition with
other WARN_ONs, as shown by this report.

>
> >
> > Fixes: b753522bed0b ("kho: add test for kexec handover")
> >
>
> Nit: these blank lines would probably mess up trailer parsing for
> tooling.

Hm, if so,  the blank line should be removed.

Thank you,
Pasha

>
> > Reported-by: kernel test robot <oliver.sang@...el.com>
> > Closes: https://lore.kernel.org/oe-lkp/202511061629.e242724-lkp@intel.com
> >
> > Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
> > ---
> >  lib/test_kho.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/lib/test_kho.c b/lib/test_kho.c
> > index 025ea251a186..85b60d87a50a 100644
> > --- a/lib/test_kho.c
> > +++ b/lib/test_kho.c
> > @@ -315,6 +315,9 @@ static int __init kho_test_init(void)
> >       phys_addr_t fdt_phys;
> >       int err;
> >
> > +     if (!kho_is_enabled())
> > +             return 0;
> > +
> >       err = kho_retrieve_subtree(KHO_TEST_FDT, &fdt_phys);
> >       if (!err)
> >               return kho_test_restore(fdt_phys);
>
> --
> Regards,
> Pratyush Yadav