linux-kernel - Re: [PATCH 5/8] x86,tracing: Mark debug_stack_{set

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Message-ID: <20200212092539.135934e1@gandalf.local.home>
Date:   Wed, 12 Feb 2020 09:25:39 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        mingo@...nel.org, joel@...lfernandes.org,
        gregkh@...uxfoundation.org, gustavo@...eddedor.com,
        tglx@...utronix.de, paulmck@...nel.org, josh@...htriplett.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com
Subject: Re: [PATCH 5/8] x86,tracing: Mark debug_stack_{set_zero,reset)()
 notrace

On Wed, 12 Feb 2020 10:32:15 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> Because do_nmi() must not call into tracing outside of
> nmi_enter()/nmi_exit(), these functions must be notrace.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  arch/x86/kernel/cpu/common.c |    4 ++--
>  arch/x86/kernel/nmi.c        |    6 ++++++
>  2 files changed, 8 insertions(+), 2 deletions(-)
> 
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c

This entire file is notrace:

 arch/x86/kernel/cpu/Makefile:

   CFLAGS_REMOVE_common.o = -pg

-- Steve

> @@ -1690,14 +1690,14 @@ void syscall_init(void)
>  DEFINE_PER_CPU(int, debug_stack_usage);
>  DEFINE_PER_CPU(u32, debug_idt_ctr);
>  
> -void debug_stack_set_zero(void)
> +void notrace debug_stack_set_zero(void)
>  {
>  	this_cpu_inc(debug_idt_ctr);
>  	load_current_idt();
>  }
>  NOKPROBE_SYMBOL(debug_stack_set_zero);
>  
> -void debug_stack_reset(void)
> +void notrace debug_stack_reset(void)
>  {
>  	if (WARN_ON(!this_cpu_read(debug_idt_ctr)))
>  		return;
> --- a/arch/x86/kernel/nmi.c
> +++ b/arch/x86/kernel/nmi.c
> @@ -534,6 +534,9 @@ do_nmi(struct pt_regs *regs, long error_
>  	}
>  #endif
>  
> +	/*
> +	 * It is important that no tracing happens before nmi_enter()!
> +	 */
>  	nmi_enter();
>  
>  	inc_irq_stat(__nmi_count);
> @@ -542,6 +545,9 @@ do_nmi(struct pt_regs *regs, long error_
>  		default_do_nmi(regs);
>  
>  	nmi_exit();
> +	/*
> +	 * No tracing after nmi_exit()!
> +	 */
>  
>  #ifdef CONFIG_X86_64
>  	if (unlikely(this_cpu_read(update_debug_stack))) {
>