linux-kernel - Re: mmotm 2017-08-25-15-50 uploaded

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Date:   Mon, 28 Aug 2017 10:31:57 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Stephen Rothwell <sfr@...b.auug.org.au>
Cc:     Randy Dunlap <rdunlap@...radead.org>, akpm@...ux-foundation.org,
        mm-commits@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-next@...r.kernel.org, broonie@...nel.org,
        Jérôme Glisse <jglisse@...hat.com>
Subject: Re: mmotm 2017-08-25-15-50 uploaded

On Mon 28-08-17 18:27:05, Stephen Rothwell wrote:
> Hi Michal,
> 
> On Mon, 28 Aug 2017 09:59:31 +0200 Michal Hocko <mhocko@...nel.org> wrote:
> >
> > From 31d551dbcb1b7987a4cd07767c1e2805849b7a26 Mon Sep 17 00:00:00 2001
> > From: Michal Hocko <mhocko@...e.com>
> > Date: Mon, 28 Aug 2017 09:41:39 +0200
> > Subject: [PATCH] 
> >  mm-hmm-struct-hmm-is-only-use-by-hmm-mirror-functionality-v2-fix
> > 
> > Compiler is complaining for allnoconfig
> > 
> > kernel/fork.c: In function 'mm_init':
> > kernel/fork.c:814:2: error: implicit declaration of function 'hmm_mm_init' [-Werror=implicit-function-declaration]
> >   hmm_mm_init(mm);
> >   ^
> > kernel/fork.c: In function '__mmdrop':
> > kernel/fork.c:893:2: error: implicit declaration of function 'hmm_mm_destroy' [-Werror=implicit-function-declaration]
> >   hmm_mm_destroy(mm);
> > 
> > Make sure that hmm_mm_init/hmm_mm_destroy empty stups are defined when
> > CONFIG_HMM is disabled.
> > 
> > Signed-off-by: Michal Hocko <mhocko@...e.com>
> > ---
> >  include/linux/hmm.h | 7 +++----
> >  1 file changed, 3 insertions(+), 4 deletions(-)
> > 
> > diff --git a/include/linux/hmm.h b/include/linux/hmm.h
> > index 9583d9a15f9c..aeb94e682dda 100644
> > --- a/include/linux/hmm.h
> > +++ b/include/linux/hmm.h
> > @@ -508,11 +508,10 @@ static inline void hmm_mm_init(struct mm_struct *mm)
> >  {
> >  	mm->hmm = NULL;
> >  }
> > -#else /* IS_ENABLED(CONFIG_HMM_MIRROR) */
> > +#endif
> > +
> > +#else /* IS_ENABLED(CONFIG_HMM) */
> >  static inline void hmm_mm_destroy(struct mm_struct *mm) {}
> >  static inline void hmm_mm_init(struct mm_struct *mm) {}
> > -#endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */
> > -
> > -
> >  #endif /* IS_ENABLED(CONFIG_HMM) */
> >  #endif /* LINUX_HMM_H */
> 
> What happens when CONFIG_HMM is defined but CONFIG_HMM_MIRROR is not?
> Or is that not possible (in which case why would we have
> CONFIG_HMM_MIRROR)? 

This is something to Jerome to answer but hmm_mm_init/hmm_mm_destroy are
used regardless of the specific HMM configuration so an empty stub
should be defined unconditionally AFAIU.
-- 
Michal Hocko
SUSE Labs