diff mbox series

[V6,02/20] trace/osnoise: Improve comments about barrier need for NMI callbacks

Message ID 17c9b30b50e304269f08be3cbf8ca8188d2ebf7e.1635284863.git.bristot@kernel.org (mailing list archive)
State Superseded
Headers show
Series RTLA: An interface for osnoise/timerlat tracers | expand

Commit Message

Daniel Bristot de Oliveira Oct. 26, 2021, 10:06 p.m. UTC 
trace_osnoise_callback_enabled is used by ftrace_nmi_enter/exit()
to know when to call the NMI callback. The barrier is used to
avoid having callbacks enabled before the resetting date during
the start or to touch the values after stopping the tracer.

Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Clark Williams <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Daniel Bristot de Oliveira <bristot@kernel.org>
Cc: linux-rt-users@vger.kernel.org
Cc: linux-trace-devel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
---
 kernel/trace/trace_osnoise.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 73f9609cba3d..f941a322ca89 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -1929,8 +1929,10 @@  static int __osnoise_tracer_start(struct trace_array *tr)
 	retval = osnoise_hook_events();
 	if (retval)
 		return retval;
+
 	/*
-	 * Make sure NMIs see reseted values.
+	 * Make sure that ftrace_nmi_enter/exit() see reset values
+	 * before enabling trace_osnoise_callback_enabled.
 	 */
 	barrier();
 	trace_osnoise_callback_enabled = true;
@@ -1965,6 +1967,10 @@  static void osnoise_tracer_stop(struct trace_array *tr)
 		return;
 
 	trace_osnoise_callback_enabled = false;
+	/*
+	 * Make sure that ftrace_nmi_enter/exit() see
+	 * trace_osnoise_callback_enabled as false before continuing.
+	 */
 	barrier();
 
 	stop_per_cpu_kthreads();