tracing: Fix initialization failure path in tracing_set_tracer()

If tracer->init() fails, current code will leave current_tracer pointing
to an unusable tracer, which at best makes 'current_tracer' report
inaccurate value.

Fix the issue by pointing current_tracer to nop tracer, and only update
current_tracer with the new one after all the initialization succeeds.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 49249c28690d..44ee11e31b82 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3172,10 +3172,10 @@ static int tracing_set_tracer(const char *buf)
         }
         destroy_trace_option_files(topts);
 
-        current_trace = t;
+        current_trace = &nop_trace;
 
-        topts = create_trace_option_files(current_trace);
-        if (current_trace->use_max_tr) {
+        topts = create_trace_option_files(t);
+        if (t->use_max_tr) {
                 int cpu;
                 /* we need to make per cpu buffer sizes equivalent */
                 for_each_tracing_cpu(cpu) {
@@ -3195,6 +3195,7 @@ static int tracing_set_tracer(const char *buf)
                         goto out;
         }
 
+        current_trace = t;
         trace_branch_enable(tr);
  out:
         mutex_unlock(&trace_types_lock);