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Message-Id: <20230117233113.2fda1900e48969bebd0d1604@kernel.org>
Date: Tue, 17 Jan 2023 23:31:13 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] trace,hardirq: No moar _rcuidle() tracing
On Tue, 17 Jan 2023 10:17:16 +0100
Ingo Molnar <mingo@...nel.org> wrote:
>
> * Peter Zijlstra <peterz@...radead.org> wrote:
>
> > On Tue, Jan 17, 2023 at 01:24:46PM +0900, Masami Hiramatsu wrote:
> > > Hi Peter,
> > >
> > > On Thu, 12 Jan 2023 20:43:49 +0100
> > > Peter Zijlstra <peterz@...radead.org> wrote:
> > >
> > > > Robot reported that trace_hardirqs_{on,off}() tickle the forbidden
> > > > _rcuidle() tracepoint through local_irq_{en,dis}able().
> > > >
> > > > For 'sane' configs, these calls will only happen with RCU enabled and
> > > > as such can use the regular tracepoint. This also means it's possible
> > > > to trace them from NMI context again.
> > > >
> > > > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > >
> > > The code looks good to me. I just have a question about comment.
> > >
> > > > ---
> > > > kernel/trace/trace_preemptirq.c | 21 +++++++++++++--------
> > > > 1 file changed, 13 insertions(+), 8 deletions(-)
> > > >
> > > > --- a/kernel/trace/trace_preemptirq.c
> > > > +++ b/kernel/trace/trace_preemptirq.c
> > > > @@ -20,6 +20,15 @@
> > > > static DEFINE_PER_CPU(int, tracing_irq_cpu);
> > > >
> > > > /*
> > > > + * ...
> > >
> > > Is this intended? Wouldn't you leave any comment here?
> >
> > I indeed forgot to write the comment before posting, my bad :/ Ingo fixed
> > it up when he applied.
>
> For completeness, I've attached the final commit, which has this comment
> included:
>
> +/*
> + * Use regular trace points on architectures that implement noinstr
> + * tooling: these calls will only happen with RCU enabled, which can
> + * use a regular tracepoint.
> + *
> + * On older architectures, use the rcuidle tracing methods (which
> + * aren't NMI-safe - so exclude NMI contexts):
> + */
Thanks! This looks good to me.
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
>
> Thanks,
>
> Ingo
>
> ================>
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Thu, 12 Jan 2023 20:43:49 +0100
> Subject: [PATCH] tracing, hardirq: No moar _rcuidle() tracing
>
> Robot reported that trace_hardirqs_{on,off}() tickle the forbidden
> _rcuidle() tracepoint through local_irq_{en,dis}able().
>
> For 'sane' configs, these calls will only happen with RCU enabled and
> as such can use the regular tracepoint. This also means it's possible
> to trace them from NMI context again.
>
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Signed-off-by: Ingo Molnar <mingo@...nel.org>
> Link: https://lore.kernel.org/r/20230112195541.477416709@infradead.org
> ---
> kernel/trace/trace_preemptirq.c | 26 ++++++++++++++++++--------
> 1 file changed, 18 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/trace/trace_preemptirq.c b/kernel/trace/trace_preemptirq.c
> index 629f2854e12b..f992444a0b1f 100644
> --- a/kernel/trace/trace_preemptirq.c
> +++ b/kernel/trace/trace_preemptirq.c
> @@ -19,6 +19,20 @@
> /* Per-cpu variable to prevent redundant calls when IRQs already off */
> static DEFINE_PER_CPU(int, tracing_irq_cpu);
>
> +/*
> + * Use regular trace points on architectures that implement noinstr
> + * tooling: these calls will only happen with RCU enabled, which can
> + * use a regular tracepoint.
> + *
> + * On older architectures, use the rcuidle tracing methods (which
> + * aren't NMI-safe - so exclude NMI contexts):
> + */
> +#ifdef CONFIG_ARCH_WANTS_NO_INSTR
> +#define trace(point) trace_##point
> +#else
> +#define trace(point) if (!in_nmi()) trace_##point##_rcuidle
> +#endif
> +
> /*
> * Like trace_hardirqs_on() but without the lockdep invocation. This is
> * used in the low level entry code where the ordering vs. RCU is important
> @@ -28,8 +42,7 @@ static DEFINE_PER_CPU(int, tracing_irq_cpu);
> void trace_hardirqs_on_prepare(void)
> {
> if (this_cpu_read(tracing_irq_cpu)) {
> - if (!in_nmi())
> - trace_irq_enable(CALLER_ADDR0, CALLER_ADDR1);
> + trace(irq_enable)(CALLER_ADDR0, CALLER_ADDR1);
> tracer_hardirqs_on(CALLER_ADDR0, CALLER_ADDR1);
> this_cpu_write(tracing_irq_cpu, 0);
> }
> @@ -40,8 +53,7 @@ NOKPROBE_SYMBOL(trace_hardirqs_on_prepare);
> void trace_hardirqs_on(void)
> {
> if (this_cpu_read(tracing_irq_cpu)) {
> - if (!in_nmi())
> - trace_irq_enable_rcuidle(CALLER_ADDR0, CALLER_ADDR1);
> + trace(irq_enable)(CALLER_ADDR0, CALLER_ADDR1);
> tracer_hardirqs_on(CALLER_ADDR0, CALLER_ADDR1);
> this_cpu_write(tracing_irq_cpu, 0);
> }
> @@ -63,8 +75,7 @@ void trace_hardirqs_off_finish(void)
> if (!this_cpu_read(tracing_irq_cpu)) {
> this_cpu_write(tracing_irq_cpu, 1);
> tracer_hardirqs_off(CALLER_ADDR0, CALLER_ADDR1);
> - if (!in_nmi())
> - trace_irq_disable(CALLER_ADDR0, CALLER_ADDR1);
> + trace(irq_disable)(CALLER_ADDR0, CALLER_ADDR1);
> }
>
> }
> @@ -78,8 +89,7 @@ void trace_hardirqs_off(void)
> if (!this_cpu_read(tracing_irq_cpu)) {
> this_cpu_write(tracing_irq_cpu, 1);
> tracer_hardirqs_off(CALLER_ADDR0, CALLER_ADDR1);
> - if (!in_nmi())
> - trace_irq_disable_rcuidle(CALLER_ADDR0, CALLER_ADDR1);
> + trace(irq_disable)(CALLER_ADDR0, CALLER_ADDR1);
> }
> }
> EXPORT_SYMBOL(trace_hardirqs_off);
--
Masami Hiramatsu (Google) <mhiramat@...nel.org>
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