kprobes: Fix to init kprobes in subsys_initcall

Since arm64 kernel initializes breakpoint trap vector in arch_initcall(),
initializing kprobe (and run smoke test) in postcore_initcall() causes
a kernel panic.

To fix this issue, move the kprobe initialization in subsys_initcall()
(which is called right afer the arch_initcall).

In-kernel kprobe users (ftrace and bpf) are using fs_initcall() which is
called after subsys_initcall(), so this shouldn't cause more problem.

Link: http://lkml.kernel.org/r/155956708268.12228.10363800793132214198.stgit@devnote2
Link: http://lkml.kernel.org/r/20190709153755.GB10123@lakrids.cambridge.arm.comReported-by: Anders Roxell <anders.roxell@linaro.org>
Fixes: b5f8b32c ("kprobes: Initialize kprobes at postcore_initcall")
Tested-by: Anders Roxell <anders.roxell@linaro.org>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/kprobes.c

@@ -2289,7 +2289,7 @@ static int __init init_kprobes(void)
 		init_test_probes();
 	return err;
 }
-postcore_initcall(init_kprobes);
+subsys_initcall(init_kprobes);
 
 #ifdef CONFIG_DEBUG_FS
 static void report_probe(struct seq_file *pi, struct kprobe *p,