Commit f143641b authored Aug 01, 2018 by Steven Rostedt (VMware)

tracing: Do not call start/stop() functions when tracing_on does not change

Currently, when one echo's in 1 into tracing_on, the current tracer's
"start()" function is executed, even if tracing_on was already one. This can
lead to strange side effects. One being that if the hwlat tracer is enabled,
and someone does "echo 1 > tracing_on" into tracing_on, the hwlat tracer's
start() function is called again which will recreate another kernel thread,
and make it unable to remove the old one.

Link: http://lkml.kernel.org/r/1533120354-22923-1-git-send-email-erica.bugden@linutronix.de

Cc: stable@vger.kernel.org
Fixes: 2df8f8a6 ("tracing: Fix regression with irqsoff tracer and tracing_on file")
Reported-by: Erica Bugden <erica.bugden@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

parent 5248ee85

kernel/trace/trace.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -7628,7 +7628,9 @@ rb_simple_write(struct file filp, const char __user ubuf,

		if (buffer) {
		mutex_lock(&trace_types_lock);
		if (val) {
		if (!!val == tracer_tracing_is_on(tr)) {
		val = 0; /* do nothing */
		} else if (val) {
		tracer_tracing_on(tr);
		if (tr->current_trace->start)
		tr->current_trace->start(tr);

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