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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: 2df8f8a6a8 ("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>
This commit is contained in:
Steven Rostedt (VMware) 2018-08-01 15:40:57 -04:00
parent 5248ee8560
commit f143641bfe
1 changed files with 3 additions and 1 deletions
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4
kernel/trace/trace.c
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@ -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);