Re: [BUG] tracing: dynamic ftrace selftest detected failures

Steven Rostedt
2024-08-21T15:49:33Z

On Wed, 21 Aug 2024 16:42:07 +0100
Mark Rutland <mark.rutland@arm.com> wrote:

> FWIW, that was in samples/ftrace/ftrace-ops.c, where tracee_relevant() and
> tracee_irrelevant() have the barrier():
>
> | /*
> | * Marked as noinline to ensure that an out-of-line traceable copy is
> | * generated by the compiler.
> | *
> | * The barrier() ensures the compiler won't elide calls by determining there
> | * are no side-effects.
> | */
> | static noinline void tracee_relevant(void)
> | {
> | barrier();
> | }
>
> ... so we already have precedent for that in tracing code.

If adding a barrier() fixes things, then I'm 100% for adding them.

Masami, does this fix it?

-- Steve

diff --git a/kernel/trace/trace_selftest_dynamic.c b/kernel/trace/trace_selftest_dynamic.c
index c364cf777e1a..a112433d78ce 100644
--- a/kernel/trace/trace_selftest_dynamic.c
+++ b/kernel/trace/trace_selftest_dynamic.c
@@ -4,12 +4,20 @@

noinline __noclone int DYN_FTRACE_TEST_NAME(void)
{
- /* used to call mcount */
+ /*
+ * Used to test function tracing. Make sure the compiler doesn't
+ * remove it.
+ */
+ barrier();
return 0;
}

noinline __noclone int DYN_FTRACE_TEST_NAME2(void)
{
- /* used to call mcount */
+ /*
+ * Used to test function tracing. Make sure the compiler doesn't
+ * remove it.
+ */
+ barrier();
return 0;
}