linux-kernel - Re: [PATCH v10 06/11] arm64: Make profile_pc() use arch_stack

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Date:   Wed, 27 Oct 2021 14:32:12 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     madvenka@...ux.microsoft.com
Cc:     broonie@...nel.org, jpoimboe@...hat.com, ardb@...nel.org,
        nobuta.keiya@...itsu.com, sjitindarsingh@...il.com,
        catalin.marinas@....com, will@...nel.org, jmorris@...ei.org,
        linux-arm-kernel@...ts.infradead.org,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 06/11] arm64: Make profile_pc() use arch_stack_walk()

On Thu, Oct 14, 2021 at 09:58:42PM -0500, madvenka@...ux.microsoft.com wrote:
> From: "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
> 
> Currently, profile_pc() in ARM64 code walks the stack using
> start_backtrace() and unwind_frame(). Make it use arch_stack_walk()
> instead. This makes maintenance easier.
> 
> Signed-off-by: Madhavan T. Venkataraman <madvenka@...ux.microsoft.com>
> ---
>  arch/arm64/kernel/time.c | 22 +++++++++++++---------
>  1 file changed, 13 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/arm64/kernel/time.c b/arch/arm64/kernel/time.c
> index eebbc8d7123e..671b3038a772 100644
> --- a/arch/arm64/kernel/time.c
> +++ b/arch/arm64/kernel/time.c
> @@ -32,22 +32,26 @@
>  #include <asm/stacktrace.h>
>  #include <asm/paravirt.h>
>  
> +static bool profile_pc_cb(void *arg, unsigned long pc)
> +{
> +	unsigned long *prof_pc = arg;
> +
> +	if (in_lock_functions(pc))
> +		return true;
> +	*prof_pc = pc;
> +	return false;
> +}
> +
>  unsigned long profile_pc(struct pt_regs *regs)
>  {
> -	struct stackframe frame;
> +	unsigned long prof_pc = 0;
>  
>  	if (!in_lock_functions(regs->pc))
>  		return regs->pc;

This can go -- the first call to profile_pc_cb() will use regs->pc.

With that gone, and the include updates to use <linux/stacktrace.h>:

Reviewed-by: Mark Rutland <mark.rutland@....com>

Mark.

> -	start_backtrace(&frame, regs->regs[29], regs->pc);
> -
> -	do {
> -		int ret = unwind_frame(NULL, &frame);
> -		if (ret < 0)
> -			return 0;
> -	} while (in_lock_functions(frame.pc));
> +	arch_stack_walk(profile_pc_cb, &prof_pc, current, regs);
>  
> -	return frame.pc;
> +	return prof_pc;
>  }
>  EXPORT_SYMBOL(profile_pc);
>  
> -- 
> 2.25.1
>