tracing: Use trace_sched_process_free() instead of exit() for pid tracing

On exit, if a process is preempted after the trace_sched_process_exit()
tracepoint but before the process is done exiting, then when it gets
scheduled in, the function tracers will not filter it properly against the
function tracing pid filters.

That is because the function tracing pid filters hooks to the
sched_process_exit() tracepoint to remove the exiting task's pid from the
filter list. Because the filtering happens at the sched_switch tracepoint,
when the exiting task schedules back in to finish up the exit, it will no
longer be in the function pid filtering tables.

This was noticeable in the notrace self tests on a preemptable kernel, as
the tests would fail as it exits and preempted after being taken off the
notrace filter table and on scheduling back in it would not be in the
notrace list, and then the ending of the exit function would trace. The test
detected this and would fail.

Cc: stable@vger.kernel.org
Cc: Namhyung Kim <namhyung@kernel.org>
Fixes: 1e10486ffee0a ("ftrace: Add 'function-fork' trace option")
Fixes: c37775d57830a ("tracing: Add infrastructure to allow set_event_pid to follow children"
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 4e3a5d79c0786928a8f503f440ec3cca0bded337..76f2dd6fd41417ec1ac25c54c1f968758e89e5b6 100644 (file)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -6985,12 +6985,12 @@ void ftrace_pid_follow_fork(struct trace_array *tr, bool enable)
        if (enable) {
                register_trace_sched_process_fork(ftrace_pid_follow_sched_process_fork,
                                                  tr);
-               register_trace_sched_process_exit(ftrace_pid_follow_sched_process_exit,
+               register_trace_sched_process_free(ftrace_pid_follow_sched_process_exit,
                                                  tr);
        } else {
                unregister_trace_sched_process_fork(ftrace_pid_follow_sched_process_fork,
                                                    tr);
-               unregister_trace_sched_process_exit(ftrace_pid_follow_sched_process_exit,
+               unregister_trace_sched_process_free(ftrace_pid_follow_sched_process_exit,
                                                    tr);
        }
 }

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index f6f55682d3e2d027b9e8127a01efbf2cb2317eb1..a85effb2373bf0eb56fcf65df288a620481cbe6c 100644 (file)
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -538,12 +538,12 @@ void trace_event_follow_fork(struct trace_array *tr, bool enable)
        if (enable) {
                register_trace_prio_sched_process_fork(event_filter_pid_sched_process_fork,
                                                       tr, INT_MIN);
-               register_trace_prio_sched_process_exit(event_filter_pid_sched_process_exit,
+               register_trace_prio_sched_process_free(event_filter_pid_sched_process_exit,
                                                       tr, INT_MAX);
        } else {
                unregister_trace_sched_process_fork(event_filter_pid_sched_process_fork,
                                                    tr);
-               unregister_trace_sched_process_exit(event_filter_pid_sched_process_exit,
+               unregister_trace_sched_process_free(event_filter_pid_sched_process_exit,
                                                    tr);
        }
 }