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Message-ID: <YzxrJYjKxy/vUc5n@FVFF77S0Q05N.cambridge.arm.com>
Date: Tue, 4 Oct 2022 18:19:33 +0100
From: Mark Rutland <mark.rutland@....com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: richard.henderson@...aro.org, ink@...assic.park.msu.ru,
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Subject: Re: [PATCH v2 33/44] ftrace: WARN on rcuidle
On Mon, Sep 19, 2022 at 12:00:12PM +0200, Peter Zijlstra wrote:
> CONFIG_GENERIC_ENTRY disallows any and all tracing when RCU isn't
> enabled.
>
> XXX if s390 (the only other GENERIC_ENTRY user as of this writing)
> isn't comfortable with this, we could switch to
> HAVE_NOINSTR_VALIDATION which is x86_64 only atm.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
> include/linux/tracepoint.h | 13 ++++++++++++-
> kernel/trace/trace.c | 3 +++
> 2 files changed, 15 insertions(+), 1 deletion(-)
>
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -178,6 +178,16 @@ static inline struct tracepoint *tracepo
> #endif /* CONFIG_HAVE_STATIC_CALL */
>
> /*
> + * CONFIG_GENERIC_ENTRY archs are expected to have sanitized entry and idle
> + * code that disallow any/all tracing/instrumentation when RCU isn't watching.
> + */
> +#ifdef CONFIG_GENERIC_ENTRY
> +#define RCUIDLE_COND(rcuidle) (rcuidle)
> +#else
> +#define RCUIDLE_COND(rcuidle) (rcuidle && in_nmi())
> +#endif
Could we make this depend on ARCH_WANTS_NO_INSTR instead?
That'll allow arm64 to check this even though we're not using the generic entry
code (and there's lots of work necessary to make that possible...).
Thanks,
Mark.
> +
> +/*
> * it_func[0] is never NULL because there is at least one element in the array
> * when the array itself is non NULL.
> */
> @@ -189,7 +199,8 @@ static inline struct tracepoint *tracepo
> return; \
> \
> /* srcu can't be used from NMI */ \
> - WARN_ON_ONCE(rcuidle && in_nmi()); \
> + if (WARN_ON_ONCE(RCUIDLE_COND(rcuidle))) \
> + return; \
> \
> /* keep srcu and sched-rcu usage consistent */ \
> preempt_disable_notrace(); \
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -3104,6 +3104,9 @@ void __trace_stack(struct trace_array *t
> return;
> }
>
> + if (WARN_ON_ONCE(IS_ENABLED(CONFIG_GENERIC_ENTRY)))
> + return;
> +
> /*
> * When an NMI triggers, RCU is enabled via ct_nmi_enter(),
> * but if the above rcu_is_watching() failed, then the NMI
>
>
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