make sure that we always have a return path from kernel_execve()

The only place where kernel_execve() is called without a way to
return to the caller of kernel_thread() callback is kernel_post().
Reorganize kernel_init()/kernel_post() - instead of the former
calling the latter in the end (and getting freed by it), have the
latter *begin* with calling the former (and turn the latter into
kernel_thread() callback, of course).
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

init/main.c

@@ -794,11 +794,11 @@ static void run_init_process(const char *init_filename)
 	kernel_execve(init_filename, argv_init, envp_init);
 }
 
-/* This is a non __init function. Force it to be noinline otherwise gcc
- * makes it inline to init() and it becomes part of init.text section
- */
-static noinline int init_post(void)
+static void __init kernel_init_freeable(void);
+
+static int __ref kernel_init(void *unused)
 {
+	kernel_init_freeable();
 	/* need to finish all async __init code before freeing the memory */
 	async_synchronize_full();
 	free_initmem();
@@ -835,7 +835,7 @@ static noinline int init_post(void)
 	      "See Linux Documentation/init.txt for guidance.");
 }
 
-static int __init kernel_init(void * unused)
+static void __init kernel_init_freeable(void)
 {
 	/*
 	 * Wait until kthreadd is all set-up.
@@ -890,7 +890,4 @@ static int __init kernel_init(void * unused)
 	 * we're essentially up and running. Get rid of the
 	 * initmem segments and start the user-mode stuff..
 	 */
-
-	init_post();
-	return 0;
 }