linux-kernel - Re: [PATCH] refcount: always allow checked forms

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Message-ID: <20180711054421.qgsdctwtncr32r4y@salmiak>
Date:   Wed, 11 Jul 2018 06:44:21 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Kees Cook <keescook@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        David Sterba <dsterba@...e.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH] refcount: always allow checked forms

On Tue, Jul 03, 2018 at 11:30:38AM -0700, Kees Cook wrote:
> On Tue, Jul 3, 2018 at 3:01 AM, Mark Rutland <mark.rutland@....com> wrote:
> > In many cases, it would be useful to be able to use the full
> > sanity-checked refcount helpers regardless of CONFIG_REFCOUNT_FULL, as
> > this would help to avoid duplicate warnings where callers try to
> > sanity-check refcount manipulation.
> >
> > This patch refactors things such that the full refcount helpers were
> > always built, as refcount_${op}_checked(), such that they can be used
> > regardless of CONFIG_REFCOUNT_FULL. This will allow code which *always*
> > wants a checked refcount to opt-in, avoiding the need to duplicate the
> > logic for warnings.
> >
> > There should be no functional change as a result of this patch.
> >
> > Signed-off-by: Mark Rutland <mark.rutland@....com>
> > Cc: Boqun Feng <boqun.feng@...il.com>
> > Cc: David Sterba <dsterba@...e.com>
> > Cc: Ingo Molnar <mingo@...nel.org>
> > Cc: Kees Cook <keescook@...omium.org>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Will Deacon <will.deacon@....com>
> 
> Looks good to me! Thanks for doing this. :)

Thank David; I rather stole his thunder here.

> Acked-by: Kees Cook <keescook@...omium.org>
> 
> > ---
> >  include/linux/refcount.h | 27 +++++++++++++++++-------
> >  lib/refcount.c           | 53 +++++++++++++++++++++++-------------------------
> >  2 files changed, 45 insertions(+), 35 deletions(-)
> >
> > Dave pointed out that it would be useful to be able to opt-in to full checks
> > regardless of CONFIG_REFCOUNT_FULL, so that we can simplify callsites where we
> > always want checks. I've spotted a few of these in code which is still awaiting
> > conversion.
> 
> Yeah, I need to go through the cocci output -- Elena had several
> outstanding patches that never got picked up.
> 
> > I'm assuming that the atomics group is intended to own the refcount code, even
> > though this isn't currently the case in MAINTAINERS.
> 
> That's how it has landed in the past, yes, but if there is a
> dependency on these for code that will use it, maybe it should go that
> way?

That sounds reasonable to me. I was just wanted to be clear as to why I'd Cc'd
the atomics maintainers. :)

I'll spin a v2 with the fixup Andrea noted.

Thanks,
Mark.