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Message-ID: <20220714111749.0a802e7f@gandalf.local.home>
Date: Thu, 14 Jul 2022 11:17:49 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Petr Mladek <pmladek@...e.com>
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, 14 Jul 2022 16:53:24 +0200
Petr Mladek <pmladek@...e.com> wrote:
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -2108,7 +2108,15 @@ static u16 printk_sprint(char *text, u16 size, int facility,
> }
> }
>
> - trace_console_rcuidle(text, text_len);
> + /*
> + * trace_console_idle() is not working in NMI. printk()
> + * is used more often in NMI than in rcuidle context.
> + * Choose the less evil solution here.
> + *
> + * smp_processor_id() is reliable in rcuidle context.
> + */
> + if (!rcu_is_idle_cpu(smp_processor_id()))
> + trace_console(text, text_len);
>
> return text_len;
> }
> --
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.
-- Steve
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)
),
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