linux-kernel - Re: [PATCH 11/16] mm: consolidate the get_user

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Message-ID: <20190625115613.GB3711@ziepe.ca>
Date:   Tue, 25 Jun 2019 08:56:13 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Christoph Hellwig <hch@....de>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        "David S. Miller" <davem@...emloft.net>,
        Nicholas Piggin <npiggin@...il.com>,
        Khalid Aziz <khalid.aziz@...cle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-mips@...r.kernel.org, linux-sh@...r.kernel.org,
        sparclinux@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-mm@...ck.org, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 11/16] mm: consolidate the get_user_pages* implementations

On Tue, Jun 25, 2019 at 09:56:50AM +0200, Christoph Hellwig wrote:
> On Fri, Jun 21, 2019 at 11:41:31AM -0300, Jason Gunthorpe wrote:
> > >  static bool gup_fast_permitted(unsigned long start, unsigned long end)
> > >  {
> > > -	return true;
> > > +	return IS_ENABLED(CONFIG_HAVE_FAST_GUP) ? true : false;
> > 
> > The ?: is needed with IS_ENABLED?
> 
> It shouldn't, I'll fix it up.
> 
> > I'd suggest to revise this block a tiny bit:
> > 
> > -#ifndef gup_fast_permitted
> > +#if !IS_ENABLED(CONFIG_HAVE_FAST_GUP) || !defined(gup_fast_permitted)
> >  /*
> >   * Check if it's allowed to use __get_user_pages_fast() for the range, or
> >   * we need to fall back to the slow version:
> >   */
> > -bool gup_fast_permitted(unsigned long start, int nr_pages)
> > +static bool gup_fast_permitted(unsigned long start, int nr_pages)
> >  {
> > 
> > Just in case some future arch code mismatches the header and kconfig..
> 
> IS_ENABLED outside a function doesn't really make sense.  But I'll
> just life the IS_ENABLED(CONFIG_HAVE_FAST_GUP) checks into the two
> callers.

I often see '#if IS_ENABLED(CONFIG_X)', IIRC last I looked at that, it
was needed because the usual #ifdef CONFIG_X didn't work if the value
was =m?

Would be interested to know if that is not the right way to use
kconfig

Jason