linux-kernel - Re: [PATCH v10 02/11] arm64: Make perf_callchain_kernel() use arch_stack

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Message-ID: <YXAu2aXqBU3rO5e+@sirena.org.uk>
Date:   Wed, 20 Oct 2021 15:59:37 +0100
From:   Mark Brown <broonie@...nel.org>
To:     madvenka@...ux.microsoft.com
Cc:     mark.rutland@....com, 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 02/11] arm64: Make perf_callchain_kernel() use
 arch_stack_walk()

On Thu, Oct 14, 2021 at 09:58:38PM -0500, madvenka@...ux.microsoft.com wrote:
> From: "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
> 
> Currently, perf_callchain_kernel() in ARM64 code walks the stack using
> start_backtrace() and walk_stackframe(). Make it use arch_stack_walk()
> instead. This makes maintenance easier.

>  static bool callchain_trace(void *data, unsigned long pc)
>  {
>  	struct perf_callchain_entry_ctx *entry = data;
> -	perf_callchain_store(entry, pc);
> -	return true;
> +	return perf_callchain_store(entry, pc) == 0;
>  }

This changes us from unconditionally doing the whole walk to returning
an error if perf_callchain_store() returns an error so it's not quite a
straight transform, though since that seems like a useful improvement
which most likely  on't have any practical impact that's fine.

Reviewed-by: Mark Brown <broonie@...nel.org>

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