tracing: Do not call start/stop() functions when tracing_on does not change
authorSteven Rostedt (VMware) <rostedt@goodmis.org>
Wed, 1 Aug 2018 19:40:57 +0000 (15:40 -0400)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Sun, 9 Sep 2018 17:55:57 +0000 (19:55 +0200)
commit4c9016757e3bf695a6716946d7fd5f0f486a475a
treec198f5938352e0144c02ddc2cc3e4822949667b3
parent2b4c940dccbe29029c75a4bf7016f864425057a9
tracing: Do not call start/stop() functions when tracing_on does not change

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@linutronix.de
Cc: stable@vger.kernel.org
Fixes: 2df8f8a6a897e ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
kernel/trace/trace.c