linux-kernel - [PATCH v4 1/2] tracing: Avoid adding tracer option before update_tracer

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Date:   Tue, 26 Apr 2022 20:24:06 +0800
From:   Mark-PK Tsai <mark-pk.tsai@...iatek.com>
To:     <rostedt@...dmis.org>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>, <mark-pk.tsai@...iatek.com>,
        <matthias.bgg@...il.com>, <mingo@...hat.com>,
        <yj.chiang@...iatek.com>
Subject: [PATCH v4 1/2] tracing: Avoid adding tracer option before update_tracer_options

To prepare for support asynchronous tracer_init_tracefs initcall,
avoid calling create_trace_option_files before __update_tracer_options.
Otherwise, create_trace_option_files will show warning because
some tracers in trace_types list are already in tr->topts.

For example, hwlat_tracer call register_tracer in late_initcall,
and global_trace.dir is already created in tracing_init_dentry,
hwlat_tracer will be put into tr->topts.
Then if the __update_tracer_options is executed after hwlat_tracer
registered, create_trace_option_files find that hwlat_tracer is
already in tr->topts.

Link: https://lore.kernel.org/lkml/20220322133339.GA32582@xsang-OptiPlex-9020/
Reported-by: kernel test robot <oliver.sang@...el.com>
Signed-off-by: Mark-PK Tsai <mark-pk.tsai@...iatek.com>
---
 kernel/trace/trace.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index f4de111fa18f..0ec7b013104a 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6332,12 +6332,18 @@ static void tracing_set_nop(struct trace_array *tr)
 	tr->current_trace = &nop_trace;
 }
 
+static bool tracer_options_updated;
+
 static void add_tracer_options(struct trace_array *tr, struct tracer *t)
 {
 	/* Only enable if the directory has been created already. */
 	if (!tr->dir)
 		return;
 
+	/* Only create trace option files after update_tracer_options finish */
+	if (!tracer_options_updated)
+		return;
+
 	create_trace_option_files(tr, t);
 }
 
@@ -9176,6 +9182,7 @@ static void __update_tracer_options(struct trace_array *tr)
 static void update_tracer_options(struct trace_array *tr)
 {
 	mutex_lock(&trace_types_lock);
+	tracer_options_updated = true;
 	__update_tracer_options(tr);
 	mutex_unlock(&trace_types_lock);
 }
-- 
2.18.0