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References: <20211110202448.4054153-1-valentin.schneider@arm.com>
 <20211110202448.4054153-5-valentin.schneider@arm.com> <YYzeOQNFmuieCk3T@elver.google.com>
In-Reply-To: <YYzeOQNFmuieCk3T@elver.google.com>
From:   Marco Elver <elver@google.com>
Date:   Thu, 11 Nov 2021 10:39:49 +0100
Message-ID: <CANpmjNPvYZSSLnsg_BGfzb=Yu4bTvCp+N14FHcJfUDjDgzrywg@mail.gmail.com>
Subject: Re: [PATCH v2 4/5] kscan: Use preemption model accessors
To:     Valentin Schneider <valentin.schneider@arm.com>
Cc:     linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com,
        linuxppc-dev@lists.ozlabs.org, linux-kbuild@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Frederic Weisbecker <frederic@kernel.org>,
        Mike Galbraith <efault@gmx.de>,
        Dmitry Vyukov <dvyukov@google.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Nick Desaulniers <ndesaulniers@google.com>
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On Thu, 11 Nov 2021 at 10:11, Marco Elver <elver@google.com> wrote:
>
> Subject s/kscan/kcsan/
>
> On Wed, Nov 10, 2021 at 08:24PM +0000, Valentin Schneider wrote:
> > Per PREEMPT_DYNAMIC, checking CONFIG_PREEMPT doesn't tell you the actual
> > preemption model of the live kernel. Use the newly-introduced accessors
> > instead.
> >
> > Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
>
> Reviewed-by: Marco Elver <elver@google.com>
>
> Though it currently doesn't compile as a module due to missing
> EXPORT_SYMBOL of is_preempt*().
>
> > ---
> >  kernel/kcsan/kcsan_test.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/kcsan/kcsan_test.c b/kernel/kcsan/kcsan_test.c
> > index dc55fd5a36fc..14d811eb9a21 100644
> > --- a/kernel/kcsan/kcsan_test.c
> > +++ b/kernel/kcsan/kcsan_test.c
> > @@ -1005,13 +1005,13 @@ static const void *nthreads_gen_params(const void *prev, char *desc)
> >       else
> >               nthreads *= 2;
> >
> > -     if (!IS_ENABLED(CONFIG_PREEMPT) || !IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER)) {
> > +     if (!is_preempt_full() || !IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER)) {

In case you introduce the 5th helper I suggested
(is_preempt_full_or_rt() or whatever you'll call it), this one can be
switched, because this check really does want to know if "at least
full preemption" and not "precisely full preemption".

Thanks,
-- Marco