tracing: Fix regression with irqsoff tracer and tracing_on file

Commit 02404baf1b47 "tracing: Remove deprecated tracing_enabled file"
removed the tracing_enabled file as it never worked properly and
the tracing_on file should be used instead. But the tracing_on file
didn't call into the tracers start/stop routines like the
tracing_enabled file did. This caused trace-cmd to break when it
enabled the irqsoff tracer.

If you just did "echo irqsoff > current_tracer" then it would work
properly. But the tool trace-cmd disables tracing first by writing
"0" into the tracing_on file. Then it writes "irqsoff" into
current_tracer and then writes "1" into tracing_on. Unfortunately,
the above commit changed the irqsoff tracer to check the tracing_on
status instead of the tracing_enabled status. If it's disabled then
it does not start the tracer internals.

The problem is that writing "1" into tracing_on does not call the
tracers "start" routine like writing "1" into tracing_enabled did.
This makes the irqsoff tracer not start when using the trace-cmd
tool, and is a regression for userspace.

Simple fix is to have the tracing_on file call the tracers start()
method when being enabled (and the stop() method when disabled).

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 1bbfa0446507405d2fce92036322224170d7411e..f3ec1cfb0de16f93a9bfe7973692a9d97f25fe1e 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4817,10 +4817,17 @@ rb_simple_write(struct file *filp, const char __user *ubuf,
                return ret;
 
        if (buffer) {
-               if (val)
+               mutex_lock(&trace_types_lock);
+               if (val) {
                        ring_buffer_record_on(buffer);
-               else
+                       if (current_trace->start)
+                               current_trace->start(tr);
+               } else {
                        ring_buffer_record_off(buffer);
+                       if (current_trace->stop)
+                               current_trace->stop(tr);
+               }
+               mutex_unlock(&trace_types_lock);
        }
 
        (*ppos)++;