linux-kernel - Re: [PATCH] sched/rt, powerpc: Prepare for PREEMPT

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Date:   Tue, 10 Nov 2020 07:18:39 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Wang Qing <wangqing@...o.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Alistair Popple <alistair@...ple.id.au>,
        Jordan Niethe <jniethe5@...il.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de
Subject: Re: [PATCH] sched/rt, powerpc: Prepare for PREEMPT_RT


Quoting Wang Qing <wangqing@...o.com>:

> Add PREEMPT_RT output to die().
>
> Signed-off-by: Wang Qing <wangqing@...o.com>
> ---
>  arch/powerpc/kernel/traps.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
> index 5006dcb..6dfe567
> --- a/arch/powerpc/kernel/traps.c
> +++ b/arch/powerpc/kernel/traps.c
> @@ -258,6 +258,14 @@ static char *get_mmu_str(void)
>  	return "";
>  }
>
> +#ifdef CONFIG_PREEMPT
> +#define S_PREEMPT " PREEMPT"
> +#elif defined(CONFIG_PREEMPT_RT)
> +#define S_PREEMPT " PREEMPT_RT"
> +#else
> +#define S_PREEMPT ""
> +#endif

I don't like too much that forest of #ifdefs. IS_ENABLED() is prefered  
whenever possible.

> +
>  static int __die(const char *str, struct pt_regs *regs, long err)
>  {
>  	printk("Oops: %s, sig: %ld [#%d]\n", str, err, ++die_counter);
> @@ -265,7 +273,7 @@ static int __die(const char *str, struct pt_regs  
> *regs, long err)
>  	printk("%s PAGE_SIZE=%luK%s%s%s%s%s%s %s\n",
>  	       IS_ENABLED(CONFIG_CPU_LITTLE_ENDIAN) ? "LE" : "BE",
>  	       PAGE_SIZE / 1024, get_mmu_str(),
> -	       IS_ENABLED(CONFIG_PREEMPT) ? " PREEMPT" : "",
> +	       S_PREEMPT,
>  	       IS_ENABLED(CONFIG_SMP) ? " SMP" : "",
>  	       IS_ENABLED(CONFIG_SMP) ? (" NR_CPUS=" __stringify(NR_CPUS)) : "",
>  	       debug_pagealloc_enabled() ? " DEBUG_PAGEALLOC" : "",
> --
> 2.7.4

I'd prefer to remain in line with the existing and use IS_ENABLED()  
instead of #ifdefs, see below:

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 5006dcbe1d9f..dec7b81c72a4 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -262,10 +262,11 @@ static int __die(const char *str, struct pt_regs  
*regs, long err)
  {
  	printk("Oops: %s, sig: %ld [#%d]\n", str, err, ++die_counter);

-	printk("%s PAGE_SIZE=%luK%s%s%s%s%s%s %s\n",
+	printk("%s PAGE_SIZE=%luK%s%s%s%s%s%s%s %s\n",
  	       IS_ENABLED(CONFIG_CPU_LITTLE_ENDIAN) ? "LE" : "BE",
  	       PAGE_SIZE / 1024, get_mmu_str(),
  	       IS_ENABLED(CONFIG_PREEMPT) ? " PREEMPT" : "",
+	       IS_ENABLED(CONFIG_PREEMPT_RT) ? " PREEMPT_RT" : "",
  	       IS_ENABLED(CONFIG_SMP) ? " SMP" : "",
  	       IS_ENABLED(CONFIG_SMP) ? (" NR_CPUS=" __stringify(NR_CPUS)) : "",
  	       debug_pagealloc_enabled() ? " DEBUG_PAGEALLOC" : "",
---
Christophe