linux-kernel - Re: [PATCH] sched: Make sched_feat(x) boolean for !CONFIG_SCHED

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Date:   Tue, 23 Oct 2018 09:44:31 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     mingo@...hat.com, Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>, Phil_K97@....de,
        groeck@...omium.org
Subject: Re: [PATCH] sched: Make sched_feat(x) boolean for !CONFIG_SCHED_DEBUG

On Mon, Oct 22, 2018 at 5:41 PM Matthias Kaehlcke <mka@...omium.org> wrote:
>
> If scheduler debugging is disabled sched_feat() resolves to a constant
> value that can be non-boolean. clang raises a warning when it detects
> that a non-boolean constant is used as operand in logical expressions:
>
> kernel/sched/core.c:208:26: warning: use of logical '&&' with constant
>   operand [-Wconstant-logical-operand]
>     if ((irq_delta + steal) && sched_feat(NONTASK_CAPACITY))
>                             ^  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Convert the original expression to boolean by means of a double not
> operation.
>
> Reported-by: Philipp Klocke <Phil_K97@....de>
> Suggested-by: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Matthias Kaehlcke <mka@...omium.org>

Thanks for resending, but I'm tracking this patch in -next:
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=7e6f4c5d600c1c8e2a1d900e65cab319d9b6782e
I just cloned -next yesterday and looks like it's still there.

> ---
>  kernel/sched/sched.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 4a2e8cae63c4..b9387d35e261 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1393,7 +1393,7 @@ static const_debug __maybe_unused unsigned int sysctl_sched_features =
>         0;
>  #undef SCHED_FEAT
>
> -#define sched_feat(x) (sysctl_sched_features & (1UL << __SCHED_FEAT_##x))
> +#define sched_feat(x) (!!(sysctl_sched_features & (1UL << __SCHED_FEAT_##x)))
>
>  #endif /* SCHED_DEBUG && HAVE_JUMP_LABEL */
>
> --
> 2.19.1.568.g152ad8e336-goog
>


-- 
Thanks,
~Nick Desaulniers