tracing: Call clear_boot_tracer() at lateinit_sync

commit 4bb0f0e7 upstream.

The clear_boot_tracer function is used to reset the default_bootup_tracer
string to prevent it from being accessed after boot, as it originally points
to init data. But since clear_boot_tracer() is called via the
init_lateinit() call, it races with the initcall for registering the hwlat
tracer. If someone adds "ftrace=hwlat" to the kernel command line, depending
on how the linker sets up the text, the saved command line may be cleared,
and the hwlat tracer never is initialized.

Simply have the clear_boot_tracer() be called by initcall_lateinit_sync() as
that's for tasks to be called after lateinit.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=196551

Fixes: e7c15cd8 ("tracing: Added hardware latency tracer")
Reported-by: Zamir SUN <sztsian@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

kernel/trace/trace.c

@@ -8224,4 +8224,4 @@ __init static int clear_boot_tracer(void)
 }
 
 fs_initcall(tracer_init_tracefs);
-late_initcall(clear_boot_tracer);
+late_initcall_sync(clear_boot_tracer);