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

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Message-ID: <CANpmjNM=rSFwmJCEq6gxHZBdYKVZas4rbnd2gk8GCAEjiJ_5UQ@mail.gmail.com>
Date:   Thu, 29 Jul 2021 16:53:10 +0200
From:   Marco Elver <elver@...gle.com>
To:     Heiko Carstens <hca@...ux.ibm.com>,
        "Paul E. McKenney" <paulmck@...nel.org>
Cc:     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

+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.

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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