linux-kernel - Re: [PATCH] kcsan: use u64 instead of cycles

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Message-ID: <20210729155834.GX4397@paulmck-ThinkPad-P17-Gen-1>
Date:   Thu, 29 Jul 2021 08:58:34 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Marco Elver <elver@...gle.com>
Cc:     Heiko Carstens <hca@...ux.ibm.com>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>, kasan-dev@...glegroups.com,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [PATCH] kcsan: use u64 instead of cycles_t

On Thu, Jul 29, 2021 at 04:53:10PM +0200, Marco Elver wrote:
> +Cc: Paul
> 
> On Thu, 29 Jul 2021 at 16:28, Heiko Carstens <hca@...ux.ibm.com> wrote:
> >
> > cycles_t has a different type across architectures: unsigned int,
> > unsinged long, or unsigned long long. Depending on architecture this
> > will generate this warning:
> >
> > kernel/kcsan/debugfs.c: In function ‘microbenchmark’:
> > ./include/linux/kern_levels.h:5:25: warning: format ‘%llu’ expects argument of type ‘long long unsigned int’, but argument 3 has type ‘cycles_t’ {aka ‘long unsigned int’} [-Wformat=]
> >
> > To avoid this simple change the type of cycle to u64 in
> > microbenchmark(), since u64 is of type unsigned long long for all
> > architectures.
> >
> > Signed-off-by: Heiko Carstens <hca@...ux.ibm.com>
> 
> Acked-by: Marco Elver <elver@...gle.com>
> 
> Do you have a series adding KCSAN support for s390, i.e. would you
> like to keep it together with those changes?
> 
> Otherwise this would go the usual route through Paul's -rcu tree.

Either way, please let me know!

							Thanx, Paul

> Thanks,
> -- Marco
> 
> > ---
> >  kernel/kcsan/debugfs.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/kcsan/debugfs.c b/kernel/kcsan/debugfs.c
> > index e65de172ccf7..1d1d1b0e4248 100644
> > --- a/kernel/kcsan/debugfs.c
> > +++ b/kernel/kcsan/debugfs.c
> > @@ -64,7 +64,7 @@ static noinline void microbenchmark(unsigned long iters)
> >  {
> >         const struct kcsan_ctx ctx_save = current->kcsan_ctx;
> >         const bool was_enabled = READ_ONCE(kcsan_enabled);
> > -       cycles_t cycles;
> > +       u64 cycles;
> >
> >         /* We may have been called from an atomic region; reset context. */
> >         memset(&current->kcsan_ctx, 0, sizeof(current->kcsan_ctx));
> > --
> > 2.25.1
> >
> > --
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