Subject: Re: [PATCH 13/13] powerpc/rtas: place tracepoints in do_enter_rtas()

From: "Nicholas Piggin" <[email-masked]>
Date: Mon, 28 Nov 2022 13:07:41 +1000

On Sat Nov 19, 2022 at 1:07 AM AEST, Nathan Lynch wrote:
> Call the just-added rtas tracepoints in do_enter_rtas(), taking care
> to avoid function name lookups in the CPU offline path.
>
> Signed-off-by: Nathan Lynch <[email-masked]>
> ---
>  arch/powerpc/kernel/rtas.c | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
>
> diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
> index 198366d641d0..3487b42cfbf7 100644
> --- a/arch/powerpc/kernel/rtas.c
> +++ b/arch/powerpc/kernel/rtas.c
> @@ -38,6 +38,7 @@
>  #include <asm/page.h>
>  #include <asm/rtas.h>
>  #include <asm/time.h>
> +#include <asm/trace.h>
>  #include <asm/udbg.h>
>  
>  enum rtas_function_flags {
> @@ -525,6 +526,7 @@ void enter_rtas(unsigned long);
>  static void do_enter_rtas(struct rtas_args *args)
>  {
>  	unsigned long msr;
> +	const char *name = NULL;
>  
>  	/*
>  	 * Make sure MSR[RI] is currently enabled as it will be forced later
> @@ -537,9 +539,30 @@ static void do_enter_rtas(struct rtas_args *args)
>  
>  	hard_irq_disable(); /* Ensure MSR[EE] is disabled on PPC64 */
>  
> +	if ((trace_rtas_input_enabled() || trace_rtas_output_enabled())) {
> +		/*
> +		 * rtas_token_to_function() uses xarray which uses RCU,
> +		 * but this code can run in the CPU offline path
> +		 * (e.g. stop-self), after it's become invalid to call
> +		 * RCU APIs.
> +		 */

We can call this in real-mode via pseries_machine_check_realmode
-> fwnmi_release_errinfo, so tracing should be disabled for that
case too... Does this_cpu_set_ftrace_enabled(0) in the early
machine check handler cover that sufficiently?

Thanks,
Nick