4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> commit f143641bfef9a4a60c57af30de26c63057e7e695 upstream. 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@xxxxxxxxxxxxx Cc: stable@xxxxxxxxxxxxxxx Fixes: 2df8f8a6a897e ("tracing: Fix regression with irqsoff tracer and tracing_on file") Reported-by: Erica Bugden <erica.bugden@xxxxxxxxxxxxx> Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/trace/trace.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -6920,7 +6920,9 @@ rb_simple_write(struct file *filp, const 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);
