linux-kernel - Re: [PATCH 3/6] ftrace/x86: Warn and ignore graph tracing when RCU is disabled

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Message-ID: <Y8/u00WHGElMDjoo@hirez.programming.kicks-ass.net>
Date:   Tue, 24 Jan 2023 15:44:35 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     mingo@...nel.org, will@...nel.org, boqun.feng@...il.com,
        mark.rutland@....com, tglx@...utronix.de, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        seanjc@...gle.com, pbonzini@...hat.com, jgross@...e.com,
        srivatsa@...il.mit.edu, amakhalov@...are.com,
        pv-drivers@...are.com, mhiramat@...nel.org, wanpengli@...cent.com,
        vkuznets@...hat.com, boris.ostrovsky@...cle.com, rafael@...nel.org,
        daniel.lezcano@...aro.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com,
        vschneid@...hat.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        linux-trace-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH 3/6] ftrace/x86: Warn and ignore graph tracing when RCU
 is disabled

On Mon, Jan 23, 2023 at 05:07:53PM -0500, Steven Rostedt wrote:

> Actually, perhaps we can just add this, and all you need to do is create
> and set CONFIG_NO_RCU_TRACING (or some other name).

Elsewhere I've used CONFIG_ARCH_WANTS_NO_INSTR for this.

Anyway, I took it for a spin and it .... doesn't seems to do the job.

With my patch the first splat is

  "RCU not on for: cpuidle_poll_time+0x0/0x70"

While with yours I seems to get the endless:

  "WARNING: suspicious RCU usage"

thing. Let me see if I can figure out where it goes side-ways.