function-graph: prevent more than one tracer registering

Impact: prevent crash due to multiple function graph tracers

The function graph tracer can currently only handle a single tracer
being registered. If another tracer registers with the function
graph tracer it can crash the system.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 7847806eefef..c81a759fbf76 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2643,6 +2643,12 @@ int register_ftrace_graph(trace_func_graph_ret_t retfunc,
 
         mutex_lock(&ftrace_lock);
 
+        /* we currently allow only one tracer registered at a time */
+        if (atomic_read(&ftrace_graph_active)) {
+                ret = -EBUSY;
+                goto out;
+        }
+
         ftrace_suspend_notifier.notifier_call = ftrace_suspend_notifier_call;
         register_pm_notifier(&ftrace_suspend_notifier);