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Message-ID: <Y9ARbgtYhxSuOIlZ@FVFF77S0Q05N>
Date: Tue, 24 Jan 2023 17:12:14 +0000
From: Mark Rutland <mark.rutland@....com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>, mingo@...nel.org,
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Subject: Re: [PATCH 3/6] ftrace/x86: Warn and ignore graph tracing when RCU
is disabled
On Tue, Jan 24, 2023 at 03:44:35PM +0100, Peter Zijlstra wrote:
> 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.
Yes please; if we use CONFIG_ARCH_WANTS_NO_INSTR then arm64 will get this "for
free" once we add the missing checks (which I assume we need) in our ftrace_prepare_return().
> 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.
Hmmm... for WARN_ONCE() don't we need to wake RCU first also? I thought we
needed that at least for the printk machinery?
Thanks,
Mark.
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