linux-kernel - Re: [RFCv1 1/4] arm64: Use static key for tracing PID in CONTEXTIDR

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Date:   Thu, 21 Oct 2021 22:37:26 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     James Clark <james.clark@....com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Kees Cook <keescook@...omium.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Nicholas Piggin <npiggin@...il.com>,
        James Morse <james.morse@....com>,
        Marc Zyngier <maz@...nel.org>, Joey Gouly <joey.gouly@....com>,
        Peter Collingbourne <pcc@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Stephane Eranian <eranian@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFCv1 1/4] arm64: Use static key for tracing PID in CONTEXTIDR

Hi James,

On Thu, Oct 21, 2021 at 03:33:01PM +0100, James Clark wrote:

[...]

> > +static int __init contextidr_init(void)
> > +{
> > +	if (IS_ENABLED(CONFIG_PID_IN_CONTEXTIDR))
> > +		static_branch_inc(&contextidr_in_use);
> > +	return 0;
> > +}
> > +early_initcall(contextidr_init);
> 
> Hi Leo,
> 
> Can you skip this early_initcall() part if you do something like this:
> 
>     DECLARE_STATIC_KEY_MAYBE(CONFIG_PID_IN_CONTEXTIDR, contextidr_in_use)
> 
> It seems like there is a way to conditionally initialise it to true.

Thanks for good point!  Will test this way in next spin.

Leo