function-graph: allow unregistering twice
Steven Rostedt [Mon, 30 Mar 2009 15:11:28 +0000 (11:11 -0400)]
Impact: fix to permanent disabling of function graph tracer

There should be nothing to prevent a tracer from unregistering a
function graph callback more than once. This can simplify error paths.

But currently, the counter does not account for mulitple unregistering
of the function graph callback. If it happens, the function graph
tracer will be permanently disabled.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/ftrace.c

index 1752a63..f1ed080 100644 (file)
@@ -2719,6 +2719,9 @@ void unregister_ftrace_graph(void)
 {
        mutex_lock(&ftrace_lock);
 
+       if (!unlikely(atomic_read(&ftrace_graph_active)))
+               goto out;
+
        atomic_dec(&ftrace_graph_active);
        unregister_trace_sched_switch(ftrace_graph_probe_sched_switch);
        ftrace_graph_return = (trace_func_graph_ret_t)ftrace_stub;
@@ -2726,6 +2729,7 @@ void unregister_ftrace_graph(void)
        ftrace_shutdown(FTRACE_STOP_FUNC_RET);
        unregister_pm_notifier(&ftrace_suspend_notifier);
 
+ out:
        mutex_unlock(&ftrace_lock);
 }