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Message-ID: <20220715094016.GD24338@pathway.suse.cz>
Date: Fri, 15 Jul 2022 11:40:16 +0200
From: Petr Mladek <pmladek@...e.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: "Paul E. McKenney" <paulmck@...nel.org>,
Marco Elver <elver@...gle.com>,
John Ogness <john.ogness@...utronix.de>,
Sergey Senozhatsky <senozhatsky@...omium.org>,
linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
Thomas Gleixner <tglx@...utronix.de>,
Johannes Berg <johannes.berg@...el.com>,
Alexander Potapenko <glider@...gle.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Naresh Kamboju <naresh.kamboju@...aro.org>,
Linux Kernel Functional Testing <lkft@...aro.org>
Subject: Re: [PATCH -printk] printk, tracing: fix console tracepoint
On Thu 2022-07-14 11:17:49, Steven Rostedt wrote:
> Although printk is not really a fast path, you could do this and avoid the
> check when the trace event is not active:
>
> (Not even compiled tested)
>
> Tweaked the comment, and used raw_smp_processor_id() as I'm not sure we are
> in a preempt disabled context, and we don't care if we are not.
Makes sense.
> diff --git a/include/trace/events/printk.h b/include/trace/events/printk.h
> index 13d405b2fd8b..d0a5f63920bb 100644
> --- a/include/trace/events/printk.h
> +++ b/include/trace/events/printk.h
> @@ -7,11 +7,20 @@
>
> #include <linux/tracepoint.h>
>
> -TRACE_EVENT(console,
> +TRACE_EVENT_CONDITION(console,
> TP_PROTO(const char *text, size_t len),
>
> TP_ARGS(text, len),
>
> + /*
> + * trace_console_rcuidle() is not working in NMI. printk()
> + * is used more often in NMI than in rcuidle context.
> + * Choose the less evil solution here.
> + *
> + * raw_smp_processor_id() is reliable in rcuidle context.
> + */
> + TP_CONDITION(!rcu_is_idle_cpu(raw_smp_processor_id())),
> +
> TP_STRUCT__entry(
> __dynamic_array(char, msg, len + 1)
> ),
It looks better. I am going to test it and send as a proper patch
for review.
Thanks for help.
Best Regards,
Petr
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