tracing/ftrace: fix the check of ftrace_trace_task

Impact: fix default empty traces on function-graph-tracer

The actual ftrace_trace_task() checks if ftrace_pid_trace is allocated and return 1 if it is true.
If it is NULL, it will check the bit of pid tracing flag for the current task (which are not set by default).
So by default, a task is not traced.
Actually all tasks should be traced by default and filter_by_pid when ftrace_pid_trace is allocated.

The appropriate condition should be to return 1 if filter_by_pid is set.

Cc Steven Rostedt <[email protected]>

Signed-off-by Frederic Weisbecker <[email protected]>

---
 kernel/trace/trace.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

kernel/trace/trace.h +1 -1

index a71bbe0..5ac6970 100644
@@ -551,7 +551,7 @@ extern struct pid *ftrace_pid_trace;
 
 static inline int ftrace_trace_task(struct task_struct *task)
 {
-	if (ftrace_pid_trace)
+	if (!ftrace_pid_trace)
 		return 1;
 
 	return test_tsk_trace_trace(task);

Signature · 1 line

1.5.6.3

Quoted 8 lines · Frederic Weisbecker

Impact: fix default empty traces on function-graph-tracer

The actual ftrace_trace_task() checks if ftrace_pid_trace is allocated and return 1 if it is true. If it is NULL, it will check the bit of pid tracing flag for the current task (which are not set by default). So by default, a task is not traced. Actually all tasks should be traced by default and filter_by_pid when ftrace_pid_trace is allocated.

Heh, I thought my output look funny. The function tracer does not use it since it registers a different function. But because the graph tracer only shows the current task on switch (I did not look into trace options) I could not really test it well.

-- Steve

Acked-by Steven Rostedt <[email protected]>