From c3b6343c0dc4a76f838e25391f6f1cdb25cfbb8c Mon Sep 17 00:00:00 2001 From: Daniel Bristot de Oliveira Date: Sun, 31 Oct 2021 19:04:57 +0100 Subject: [PATCH] tracing/osnoise: Improve comments about barrier need for NMI callbacks 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. Link: https://lkml.kernel.org/r/a413b8f14aa9312fbd1ba99f96225a8aed831053.1635702894.git.bristot@kernel.org Cc: Ingo Molnar Cc: Tom Zanussi Cc: Masami Hiramatsu Cc: Juri Lelli Cc: Clark Williams Cc: John Kacur Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Sebastian Andrzej Siewior Cc: Daniel Bristot de Oliveira Cc: linux-rt-users@vger.kernel.org Cc: linux-trace-devel@vger.kernel.org Cc: linux-kernel@vger.kernel.org Suggested-by: Steven Rostedt Signed-off-by: Daniel Bristot de Oliveira Signed-off-by: Steven Rostedt (VMware) --- kernel/trace/trace_osnoise.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c index ceff407655a5..7d6be609d3dd 100644 --- a/kernel/trace/trace_osnoise.c +++ b/kernel/trace/trace_osnoise.c @@ -1930,8 +1930,10 @@ 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; @@ -1966,6 +1968,10 @@ 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(); -- GitLab