Commit 2c98c4a0 authored Aug 04, 2020 by Steven Rostedt (VMware) Committed by Greg Kroah-Hartman Aug 21, 2020

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



commit afcab636657421f7ebfa0783a91f90256bba0091 upstream.

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: 1e10486f ("ftrace: Add 'function-fork' trace option")
Fixes: c37775d5 ("tracing: Add infrastructure to allow set_event_pid to follow children"
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent b3b77736

kernel/trace/ftrace.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -6450,12 +6450,12 @@ 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);
		}
		}

kernel/trace/trace_events.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -534,12 +534,12 @@ 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);
		}
		}